B Michon; A B Kuzmenko; M K Tran; B McElfresh; S Komiya; S Ono; S Uchida; D van der Marel Spectral weight of hole-doped cuprates across the pseudogap critical point Journal Article Phys. Rev. Research, 3 , pp. 043125, 2021. @article{PhysRevResearch.3.043125, title = {Spectral weight of hole-doped cuprates across the pseudogap critical point}, author = {B Michon and A B Kuzmenko and M K Tran and B McElfresh and S Komiya and S Ono and S Uchida and D van der Marel}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.3.043125}, doi = {10.1103/PhysRevResearch.3.043125}, year = {2021}, date = {2021-11-01}, journal = {Phys. Rev. Research}, volume = {3}, pages = {043125}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Dirk van der Marel Tantalates Transcend Titanates Journal Article Journal Club for Condensed Matter Physics, 2021. @article{vanderMarel2021, title = {Tantalates Transcend Titanates}, author = {Dirk van der Marel }, editor = {Journal Club for Condensed Matter Physics}, url = {https://www.condmatjclub.org/uploads/2021/05/JCCM_May_2021_01.pdf}, doi = {https://doi.org/10.36471/JCCM_May_2021_01}, year = {2021}, date = {2021-06-01}, journal = {Journal Club for Condensed Matter Physics}, abstract = {Dirk van der Marel reports on recent additions to the numerous angels dancing on the head of a pin in the problem of superconductivity in lightly doped layers of SrTiO(3) and KTaO(3) which are near a ferroelectric quantum critical point at zero doping.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dirk van der Marel reports on recent additions to the numerous angels dancing on the head of a pin in the problem of superconductivity in lightly doped layers of SrTiO(3) and KTaO(3) which are near a ferroelectric quantum critical point at zero doping. | |
D Valentinis; J Zaanen; D van der Marel Propagation of shear stress in strongly interacting metallic Fermi liquids enhances transmission of terahertz radiation Journal Article Scientific Reports, 11 (1), 2021. @article{Valentinis2021, title = {Propagation of shear stress in strongly interacting metallic Fermi liquids enhances transmission of terahertz radiation}, author = {D Valentinis and J Zaanen and D van der Marel}, url = {https://doi.org/10.1038/s41598-021-86356-2}, doi = {10.1038/s41598-021-86356-2}, year = {2021}, date = {2021-03-29}, journal = {Scientific Reports}, volume = {11}, number = {1}, publisher = {Springer Science and Business Media LLC}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
H Meley; M Tran; J Teyssier; J A Krieger; T Prokscha; A Suter; Z Salman; M Viret; D van der Marel; S Gariglio Strain tuning of interorbital correlations in LaVO3 thin films Journal Article Physical Review B, 103 (12), 2021. @article{Meley2021, title = {Strain tuning of interorbital correlations in LaVO3 thin films}, author = {H Meley and M Tran and J Teyssier and J A Krieger and T Prokscha and A Suter and Z Salman and M Viret and D van der Marel and S Gariglio}, url = {https://doi.org/10.1103/physrevb.103.125112}, doi = {10.1103/physrevb.103.125112}, year = {2021}, date = {2021-03-05}, journal = {Physical Review B}, volume = {103}, number = {12}, publisher = {American Physical Society (APS)}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
M K Tran; A Akrap; J Levallois; J Teyssier; P Schouwink; C Besnard; P Lerch; J W Allen; M Greenblatt; D van der Marel Pressure-induced structural transitions triggering dimensional crossover in the lithium purple bronze Li0.9Mo6O17 Journal Article Physical Review B, 103 (23), 2021. @article{Tran2021, title = {Pressure-induced structural transitions triggering dimensional crossover in the lithium purple bronze Li0.9Mo6O17}, author = {M K Tran and A Akrap and J Levallois and J Teyssier and P Schouwink and C Besnard and P Lerch and J W Allen and M Greenblatt and D van der Marel}, url = {https://doi.org/10.1103/physrevb.103.235124}, doi = {10.1103/physrevb.103.235124}, year = {2021}, date = {2021-01-14}, journal = {Physical Review B}, volume = {103}, number = {23}, publisher = {American Physical Society (APS)}, abstract = {Open Data on https://yareta.unige.ch/#/home/detail/12b05553-51b5-4833-a590-801bf3352db5}, keywords = {}, pubstate = {published}, tppubtype = {article} } Open Data on https://yareta.unige.ch/#/home/detail/12b05553-51b5-4833-a590-801bf3352db5 | |
I Ardizzone; J Teyssier; I Crassee; A B Kuzmenko; D G Mazzone; D J Gawryluk; M Medarde; D van der Marel Raman spectroscopic evidence for multiferroicity in rare earth nickelate single crystals Journal Article Physical Review Research, 3 (3), 2021. @article{Ardizzone2021, title = {Raman spectroscopic evidence for multiferroicity in rare earth nickelate single crystals}, author = {I Ardizzone and J Teyssier and I Crassee and A B Kuzmenko and D G Mazzone and D J Gawryluk and M Medarde and D van der Marel}, url = {https://doi.org/10.1103/physrevresearch.3.033007}, doi = {10.1103/physrevresearch.3.033007}, year = {2021}, date = {2021-01-01}, journal = {Physical Review Research}, volume = {3}, number = {3}, publisher = {American Physical Society (APS)}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
I Ardizzone; M Zingl; J Teyssier; H U R Strand; O Peil; J Fowlie; A B Georgescu; S Catalano; N Bachar; A B Kuzmenko; M Gibert; J -M Triscone; A Georges; D van der Marel Optical properties of LaNiO3 films tuned from compressive to tensile strain Journal Article Phys. Rev. B, 102 , pp. 155148, 2020. @article{Ardizzone2020, title = {Optical properties of LaNiO3 films tuned from compressive to tensile strain}, author = {I Ardizzone and M Zingl and J Teyssier and H U R Strand and O Peil and J Fowlie and A B Georgescu and S Catalano and N Bachar and A B Kuzmenko and M Gibert and J -M Triscone and A Georges and D van der Marel}, url = {https://link.aps.org/doi/10.1103/PhysRevB.102.155148}, doi = {10.1103/PhysRevB.102.155148}, year = {2020}, date = {2020-10-01}, journal = {Phys. Rev. B}, volume = {102}, pages = {155148}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
G. Scheerer; M. Boselli; D. Pulmannova; C. W. Rischau; A. Waelchli; S. Gariglio; E. Giannini; D. van der Marel; J.-M. Triscone Ferroelectricity, Superconductivity, and SrTiO3—Passions of K.A. Müller Journal Article Condensed Matter, 5 (4), pp. 60, 2020, ISSN: 2410-3896. @article{Scheerer2020, title = {Ferroelectricity, Superconductivity, and SrTiO3—Passions of K.A. Müller}, author = {G. Scheerer and M. Boselli and D. Pulmannova and C. W. Rischau and A. Waelchli and S. Gariglio and E. Giannini and D. van der Marel and J.-M. Triscone}, url = {http://dx.doi.org/10.3390/condmat5040060}, doi = {10.3390/condmat5040060}, issn = {2410-3896}, year = {2020}, date = {2020-10-01}, journal = {Condensed Matter}, volume = {5}, number = {4}, pages = {60}, publisher = {MDPI AG}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
A Delhomme; D Vaclavkova; A Slobodeniuk; M Orlita; M Potemski; D M Basko; K Watanabe; T Taniguchi; D Mauro; C Barreteau; E Giannini; A F Morpurgo; N Ubrig; C Faugeras Flipping exciton angular momentum with chiral phonons in MoSe2/WSe2 heterobilayers Journal Article 2D Materials, 7 (4), pp. 041002, 2020. @article{Delhomme2020, title = {Flipping exciton angular momentum with chiral phonons in MoSe2/WSe2 heterobilayers}, author = {A Delhomme and D Vaclavkova and A Slobodeniuk and M Orlita and M Potemski and D M Basko and K Watanabe and T Taniguchi and D Mauro and C Barreteau and E Giannini and A F Morpurgo and N Ubrig and C Faugeras}, url = {https://doi.org/10.1088%2F2053-1583%2Faba567}, doi = {10.1088/2053-1583/aba567}, year = {2020}, date = {2020-08-01}, journal = {2D Materials}, volume = {7}, number = {4}, pages = {041002}, publisher = {IOP Publishing}, abstract = {Optical selection rules in monolayers of transition metal dichalcogenides and of their heterostructures are determined by the conservation of the z-component of the total angular momentum— JZ=LZ+SZ – associated with the C3 rotational lattice symmetry which assumes half integer values corresponding, modulo 3, to distinct states. Here we show, based on polarization resolved and low temperature magneto-optical spectroscopy experiments, that the conservation of the total angular momentum in these systems leads to a very efficient exciton-phonon interaction when the coupling is mediated through chiral phonons. We identify these phonons as the Γ point E” modes which despite carrying angular momentum ± 1 are able to induce an excitonic spin-flip of thanks to the C3 symmetry. These experiments reveal the crucial role of electron-phonon interaction in the carrier dynamics of group 6 transition metal dichalcogenides.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Optical selection rules in monolayers of transition metal dichalcogenides and of their heterostructures are determined by the conservation of the z-component of the total angular momentum— JZ=LZ+SZ – associated with the C3 rotational lattice symmetry which assumes half integer values corresponding, modulo 3, to distinct states. Here we show, based on polarization resolved and low temperature magneto-optical spectroscopy experiments, that the conservation of the total angular momentum in these systems leads to a very efficient exciton-phonon interaction when the coupling is mediated through chiral phonons. We identify these phonons as the Γ point E” modes which despite carrying angular momentum ± 1 are able to induce an excitonic spin-flip of thanks to the C3 symmetry. These experiments reveal the crucial role of electron-phonon interaction in the carrier dynamics of group 6 transition metal dichalcogenides. | |
K. Wang; B. Xu; C. W. Rischau; N. Bachar ; B. Michon; J. Teyssier ; Y. Qiu; T. Ohtsuki; Bing Cheng; N. P. Armitage; S. Nakatsuji; D. van der Marel Unconventional free charge in the correlated semimetal Nd2Ir2O7 Journal Article Nature Physics, 2020. @article{Wang2020, title = {Unconventional free charge in the correlated semimetal Nd2Ir2O7}, author = {K. Wang and B. Xu and C. W. Rischau and N. Bachar and B. Michon and J. Teyssier and Y. Qiu and T. Ohtsuki and Bing Cheng and N. P. Armitage and S. Nakatsuji and D. van der Marel }, url = {https://www.nature.com/articles/s41567-020-0955-0}, doi = {https://doi.org/10.1038/s41567-020-0955-0}, year = {2020}, date = {2020-06-29}, journal = {Nature Physics}, abstract = {Nd2Ir2O7 is a correlated semimetal with the pyrochlore structure, in which competing spin–orbit coupling and electron–electron interactions are believed to induce a time-reversal symmetry-broken Weyl semimetal phase characterized by pairs of topologically protected Dirac points at the Fermi energy. However, the emergent properties in these materials are far from clear, and exotic new states of matter have been conjectured. Here, we demonstrate optically that, at low temperatures, the free carrier spectral weight is proportional to T2, where T is the temperature, as expected for massless Dirac electrons. However, we do not observe the corresponding T3 term in the specific heat. That the system is not in a Fermi liquid state is further corroborated by the charge carrier scattering rate approaching critical damping and the progressive opening of a correlation-induced gap at low temperatures. These observations cannot be reconciled within the framework of band theory of electron-like quasiparticles and point towards the effective decoupling of the charge transport from the single particle sector.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Nd2Ir2O7 is a correlated semimetal with the pyrochlore structure, in which competing spin–orbit coupling and electron–electron interactions are believed to induce a time-reversal symmetry-broken Weyl semimetal phase characterized by pairs of topologically protected Dirac points at the Fermi energy. However, the emergent properties in these materials are far from clear, and exotic new states of matter have been conjectured. Here, we demonstrate optically that, at low temperatures, the free carrier spectral weight is proportional to T2, where T is the temperature, as expected for massless Dirac electrons. However, we do not observe the corresponding T3 term in the specific heat. That the system is not in a Fermi liquid state is further corroborated by the charge carrier scattering rate approaching critical damping and the progressive opening of a correlation-induced gap at low temperatures. These observations cannot be reconciled within the framework of band theory of electron-like quasiparticles and point towards the effective decoupling of the charge transport from the single particle sector. | |
Andrea Amoretti; Martina Meinero; Daniel K Brattan; Federico Caglieris; Enrico Giannini; Marco Affronte; Christian Hess; Bernd Buechner; Nicodemo Magnoli; Marina Putti Hydrodynamical description for magneto-transport in the strange metal phase of Bi-2201 Journal Article Phys. Rev. Research, 2 , pp. 023387, 2020. @article{Amoretti2020, title = {Hydrodynamical description for magneto-transport in the strange metal phase of Bi-2201}, author = {Andrea Amoretti and Martina Meinero and Daniel K Brattan and Federico Caglieris and Enrico Giannini and Marco Affronte and Christian Hess and Bernd Buechner and Nicodemo Magnoli and Marina Putti}, url = {https://link.aps.org/doi/10.1103/PhysRevResearch.2.023387}, doi = {10.1103/PhysRevResearch.2.023387}, year = {2020}, date = {2020-06-01}, journal = {Phys. Rev. Research}, volume = {2}, pages = {023387}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Gen Long; Hugo Henck; Marco Gibertini; Dumitru Dumcenco; Zhe Wang; Takashi Taniguchi; Kenji Watanabe; Enrico Giannini; Alberto F Morpurgo Persistence of Magnetism in Atomically Thin MnPS3 Crystals Journal Article Nano Letters, 20 (4), pp. 2452–2459, 2020, ISBN: 1530-6984. @article{Long2020, title = {Persistence of Magnetism in Atomically Thin MnPS3 Crystals}, author = {Gen Long and Hugo Henck and Marco Gibertini and Dumitru Dumcenco and Zhe Wang and Takashi Taniguchi and Kenji Watanabe and Enrico Giannini and Alberto F Morpurgo}, url = {https://doi.org/10.1021/acs.nanolett.9b05165}, doi = {10.1021/acs.nanolett.9b05165}, isbn = {1530-6984}, year = {2020}, date = {2020-04-08}, booktitle = {Nano Letters}, journal = {Nano Letters}, volume = {20}, number = {4}, pages = {2452--2459}, publisher = {American Chemical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Diego Mauro; Hugo Henck; Marco Gibertini; Michele Filippone; Enrico Giannini; Ignacio Gutierrez; Alberto F Morpurgo Multi-frequency Shubnikov-de Haas oscillations in topological semimetal Pt2HgSe3 Journal Article 2D Materials, 7 (2), pp. 025042, 2020. @article{Mauro2020b, title = {Multi-frequency Shubnikov-de Haas oscillations in topological semimetal Pt2HgSe3}, author = {Diego Mauro and Hugo Henck and Marco Gibertini and Michele Filippone and Enrico Giannini and Ignacio Gutierrez and Alberto F Morpurgo}, url = {https://doi.org/10.1088%2F2053-1583%2Fab7689}, doi = {10.1088/2053-1583/ab7689}, year = {2020}, date = {2020-03-01}, journal = {2D Materials}, volume = {7}, number = {2}, pages = {025042}, publisher = {IOP Publishing}, abstract = {Monolayer jacutingaite (Pt2HgSe3) has been recently identified as a candidate quantum spin Hall system with a 0.5 eV band gap, but no transport measurements have been performed so far on this material, neither in monolayer nor in the bulk. By using a dedicated high-pressure technique, we grow crystals enabling the exfoliation of 50-100 nm thick layers and the realization of devices for controlled transport experiments. Magnetoresistance measurements indicate that jacutingaite is a semimetal, exhibiting Shubnikov-de Haas (SdH) resistance oscillations with a multi-frequency spectrum. We adapt the Lifshitz-Kosevich formula to analyze quantitatively the SdH resistance oscillations in the presence of multiple frequencies, and find that the experimental observations are overall reproduced well by band structure ab-initio calculations for bulk jacutingaite. Together with the relatively high electron mobility extracted from the experiments (≈ 2000 cm2/V−1s−1, comparable to what is observed in WTe2 crystals of the same thickness), our results indicate that monolayer jacutingaite should provide an excellent platform to investigate transport in 2D quantum spin Hall systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Monolayer jacutingaite (Pt2HgSe3) has been recently identified as a candidate quantum spin Hall system with a 0.5 eV band gap, but no transport measurements have been performed so far on this material, neither in monolayer nor in the bulk. By using a dedicated high-pressure technique, we grow crystals enabling the exfoliation of 50-100 nm thick layers and the realization of devices for controlled transport experiments. Magnetoresistance measurements indicate that jacutingaite is a semimetal, exhibiting Shubnikov-de Haas (SdH) resistance oscillations with a multi-frequency spectrum. We adapt the Lifshitz-Kosevich formula to analyze quantitatively the SdH resistance oscillations in the presence of multiple frequencies, and find that the experimental observations are overall reproduced well by band structure ab-initio calculations for bulk jacutingaite. Together with the relatively high electron mobility extracted from the experiments (≈ 2000 cm2/V−1s−1, comparable to what is observed in WTe2 crystals of the same thickness), our results indicate that monolayer jacutingaite should provide an excellent platform to investigate transport in 2D quantum spin Hall systems. | |
I Cucchi; A Marrazzo; E Cappelli; S Ricc`o; F Y Bruno; S Lisi; M Hoesch; T K Kim; C Cacho; C Besnard; E Giannini; N Marzari; M Gibertini; F Baumberger; A Tamai Bulk and Surface Electronic Structure of the Dual-Topology Semimetal Pt2HgSe3 Journal Article Phys. Rev. Lett., 124 , pp. 106402, 2020. @article{Cucchi2020, title = {Bulk and Surface Electronic Structure of the Dual-Topology Semimetal Pt2HgSe3}, author = {I Cucchi and A Marrazzo and E Cappelli and S Ricc`o and F Y Bruno and S Lisi and M Hoesch and T K Kim and C Cacho and C Besnard and E Giannini and N Marzari and M Gibertini and F Baumberger and A Tamai}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.124.106402}, doi = {10.1103/PhysRevLett.124.106402}, year = {2020}, date = {2020-03-01}, journal = {Phys. Rev. Lett.}, volume = {124}, pages = {106402}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Bojja Aditya Reddy; Evgeniy Ponomarev; Ignacio Gutiérrez-Lezama; Nicolas Ubrig; Céline Barreteau; Enrico Giannini; Alberto F Morpurgo Synthetic Semimetals with van der Waals Interfaces Journal Article Nano Letters, 20 (2), pp. 1322–1328, 2020, ISBN: 1530-6984. @article{Reddy2020, title = {Synthetic Semimetals with van der Waals Interfaces}, author = {Bojja Aditya Reddy and Evgeniy Ponomarev and Ignacio Gutiérrez-Lezama and Nicolas Ubrig and Céline Barreteau and Enrico Giannini and Alberto F Morpurgo}, url = {https://doi.org/10.1021/acs.nanolett.9b04810}, doi = {10.1021/acs.nanolett.9b04810}, isbn = {1530-6984}, year = {2020}, date = {2020-02-12}, booktitle = {Nano Letters}, journal = {Nano Letters}, volume = {20}, number = {2}, pages = {1322--1328}, publisher = {American Chemical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Aleksandra V Zabuga; Marcelle I Arrigo; Jérémie Teyssier; Sébastien R Mouchet; Kanto Nishikawa; Masafumi Matsui; Miguel Vences; Michel C Milinkovitch Translucent in air and iridescent in water: structural analysis of a salamander egg sac Journal Article Soft Matter, pp. -, 2020. @article{C9SM02151E, title = {Translucent in air and iridescent in water: structural analysis of a salamander egg sac}, author = {Aleksandra V Zabuga and Marcelle I Arrigo and Jérémie Teyssier and Sébastien R Mouchet and Kanto Nishikawa and Masafumi Matsui and Miguel Vences and Michel C Milinkovitch}, url = {http://dx.doi.org/10.1039/C9SM02151E}, doi = {10.1039/C9SM02151E}, year = {2020}, date = {2020-01-01}, journal = {Soft Matter}, pages = {-}, publisher = {The Royal Society of Chemistry}, abstract = {Females of some Asian salamanders of the genus Hynobius deposit in streams their eggs embedded in a translucent envelope called an ‘egg sac’. The edges of the envelope exhibit a spectacular blue-to-yellow iridescent glow, which instantaneously disappears when the sac is removed from water. First, our scanning electron microscopy analyses reveal that the inner surface of the 100 μm-thick envelope displays striations (length scale of about 3 μm), which are themselves covered by much smaller (190 ± 30 nm) and quasi-periodic corrugations. The latter could constitute a surface diffraction grating generating iridescence by light interference. Second, our transmission electron microscopy and focused-ion-beam scanning electron microscopy analyses show that the bulk of the egg sac wall is composed of meandering fibres with a quasi-periodic modulation of 190 ± 60 nm along the thickness of the envelope, generating a photonic crystal. Third, Fourier power analyses of 450 electron microscopy images with varying incident angles indicate that changing the surrounding medium from water to air shifts most of the backscattered power spectrum to the ultraviolet range, hence, explaining that the egg sac loses visible iridescence when removed out of the water. Fourth, the results of our photography and optical spectroscopy experiments of submerged and emerged egg sacs rule out the possibility that the iridescence is due to a thin film or a multilayer, whereas the observed non-specular response is compatible with the backscattering expected from surface diffraction gratings and volumetric photonic crystals with spatial 1D modulation. Finally, although we mention several potential biological functions of the egg sac structural colours and iridescence, we emphasise that these optical properties might be the by-products of the envelope material internal structure selected during evolution for its mechanical properties.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Females of some Asian salamanders of the genus Hynobius deposit in streams their eggs embedded in a translucent envelope called an ‘egg sac’. The edges of the envelope exhibit a spectacular blue-to-yellow iridescent glow, which instantaneously disappears when the sac is removed from water. First, our scanning electron microscopy analyses reveal that the inner surface of the 100 μm-thick envelope displays striations (length scale of about 3 μm), which are themselves covered by much smaller (190 ± 30 nm) and quasi-periodic corrugations. The latter could constitute a surface diffraction grating generating iridescence by light interference. Second, our transmission electron microscopy and focused-ion-beam scanning electron microscopy analyses show that the bulk of the egg sac wall is composed of meandering fibres with a quasi-periodic modulation of 190 ± 60 nm along the thickness of the envelope, generating a photonic crystal. Third, Fourier power analyses of 450 electron microscopy images with varying incident angles indicate that changing the surrounding medium from water to air shifts most of the backscattered power spectrum to the ultraviolet range, hence, explaining that the egg sac loses visible iridescence when removed out of the water. Fourth, the results of our photography and optical spectroscopy experiments of submerged and emerged egg sacs rule out the possibility that the iridescence is due to a thin film or a multilayer, whereas the observed non-specular response is compatible with the backscattering expected from surface diffraction gratings and volumetric photonic crystals with spatial 1D modulation. Finally, although we mention several potential biological functions of the egg sac structural colours and iridescence, we emphasise that these optical properties might be the by-products of the envelope material internal structure selected during evolution for its mechanical properties. | |
D Matera; M Bonura; R v Cern'y; S McKeown Walker; F Buta; D LeBoeuf; X Chaud; E Giannini; C Senatore High-field superconductivity in C-doped MgB2 bulk samples prepared by a rapid synthesis route Journal Article Scientific Reports, 10 (1), pp. 17656, 2020, ISBN: 2045-2322. @article{cite-key, title = {High-field superconductivity in C-doped MgB2 bulk samples prepared by a rapid synthesis route}, author = {D Matera and M Bonura and R {v C}ern{'y} and S McKeown Walker and F Buta and D LeBoeuf and X Chaud and E Giannini and C Senatore}, url = {https://doi.org/10.1038/s41598-020-74300-9}, doi = {10.1038/s41598-020-74300-9}, isbn = {2045-2322}, year = {2020}, date = {2020-01-01}, journal = {Scientific Reports}, volume = {10}, number = {1}, pages = {17656}, abstract = {The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present between the upper-critical-field values measured in MgB2 polycrystalline bulk superconductors and those of thin films, where values as high as ~ 50 T have been achieved at 4.2 K. Filling this gap would unlock the potential of MgB2 for magnet applications. This work presents the results of an extensive experimental campaign on MgB2 bulk samples, which has been guided by a Design of Experiment. We modeled the dependence of the upper critical field on the main synthesis parameters and established a new record (~ 35 T at 4.2 K) preparing C-doped bulk samples by a non-conventional rapid-synthesis route. This value appears to be an upper boundary for the upper critical field in bulk samples. Structural disorder in films seems to act selectively on one of the two bands where superconductivity in MgB2 takes place: this enhances the upper critical field while reducing the critical temperature only by few Kelvins. On the other hand, the critical temperature in bulk samples decreases monotonically when structural disorder increases, and this imposes a limit to the maximum achievable upper critical field.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The upper critical field sets the thermodynamic limit to superconductivity. A big gap is present between the upper-critical-field values measured in MgB2 polycrystalline bulk superconductors and those of thin films, where values as high as ~ 50 T have been achieved at 4.2 K. Filling this gap would unlock the potential of MgB2 for magnet applications. This work presents the results of an extensive experimental campaign on MgB2 bulk samples, which has been guided by a Design of Experiment. We modeled the dependence of the upper critical field on the main synthesis parameters and established a new record (~ 35 T at 4.2 K) preparing C-doped bulk samples by a non-conventional rapid-synthesis route. This value appears to be an upper boundary for the upper critical field in bulk samples. Structural disorder in films seems to act selectively on one of the two bands where superconductivity in MgB2 takes place: this enhances the upper critical field while reducing the critical temperature only by few Kelvins. On the other hand, the critical temperature in bulk samples decreases monotonically when structural disorder increases, and this imposes a limit to the maximum achievable upper critical field. | |
Dumitru Dumcenco; Enrico Giannini Growth of van der Waals magnetic semiconductor materials Journal Article Journal of Crystal Growth, 548 , pp. 125799, 2020, ISSN: 0022-0248. @article{Dumcenco2020, title = {Growth of van der Waals magnetic semiconductor materials}, author = {Dumitru Dumcenco and Enrico Giannini}, url = {http://www.sciencedirect.com/science/article/pii/S0022024820303225}, doi = {https://doi.org/10.1016/j.jcrysgro.2020.125799}, issn = {0022-0248}, year = {2020}, date = {2020-01-01}, journal = {Journal of Crystal Growth}, volume = {548}, pages = {125799}, abstract = {Magnetic order in two-dimensional semiconducting layered materials is extremely rare. This has recently triggered a great interest in a variety of layered magnetic compounds, determining whether their magnetic properties can be retained down to monolayer thickness. The most promising systems are the binary MX3 and ternary MYZ3 compounds, where M is a metal, X is a halogen element, Y = Si, Ge or P, and Z is a chalcogen. The transition metal incorporates the magnetism, by a partially filled d-shell, thus enabling ferroic responses for enhanced functionalities. In most of these systems, the phase diagrams are not known and the crystal growth process is made challenging by the high fugacity of some elements and the high reaction temperature needed. We review the recent progress in crystal growth of various compounds of these families, namely CrI3, CrCl3, CrSiTe3, CrGeTe3, MnPS3 and MnPSe3, for which we used different growth techniques, such as melt growth, physical vapor transport and chemical vapor transport. The growth parameters are summarized and discussed. The characterization of the materials is focusing on the determination of the crystal structure, chemical composition and magnetic properties. In some cases, exfoliated flakes of these crystals have been successfully used for nano-device fabrication.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Magnetic order in two-dimensional semiconducting layered materials is extremely rare. This has recently triggered a great interest in a variety of layered magnetic compounds, determining whether their magnetic properties can be retained down to monolayer thickness. The most promising systems are the binary MX3 and ternary MYZ3 compounds, where M is a metal, X is a halogen element, Y = Si, Ge or P, and Z is a chalcogen. The transition metal incorporates the magnetism, by a partially filled d-shell, thus enabling ferroic responses for enhanced functionalities. In most of these systems, the phase diagrams are not known and the crystal growth process is made challenging by the high fugacity of some elements and the high reaction temperature needed. We review the recent progress in crystal growth of various compounds of these families, namely CrI3, CrCl3, CrSiTe3, CrGeTe3, MnPS3 and MnPSe3, for which we used different growth techniques, such as melt growth, physical vapor transport and chemical vapor transport. The growth parameters are summarized and discussed. The characterization of the materials is focusing on the determination of the crystal structure, chemical composition and magnetic properties. In some cases, exfoliated flakes of these crystals have been successfully used for nano-device fabrication. | |
Á. Pásztor; A. Scarfato; C. Barreteau; E. Giannini; C. Renner Dimensional cross-over of the charge density wave order parameter in thin exfoliated 1T-VSe2 Journal Article 2D Materials, 4 (4), pp. 041005, 2019. @article{Pásztor2019, title = {Dimensional cross-over of the charge density wave order parameter in thin exfoliated 1T-VSe2}, author = {Á. Pásztor and A. Scarfato and C. Barreteau and E. Giannini and C. Renner}, url = {https://doi.org/10.1088%2F2053-1583%2Faa86de}, doi = {10.1088/2053-1583/aa86de}, year = {2019}, date = {2019-09-04}, journal = {2D Materials}, volume = {4}, number = {4}, pages = {041005}, abstract = {Isolating single unit-cell thin layers from the bulk matrix of layered compounds offers tremendous opportunities to design novel functional electronic materials. However, a comprehensive thickness dependence study is paramount to harness the electronic properties of such atomic foils and their stacking into synthetic heterostructures. Here we show that a dimensional crossover and quantum confinement with reducing thickness result in a striking non-monotonic evolution of the charge density wave transition temperature in VSe2. Our conclusion is drawn from a direct derivation of the local order parameter and transition temperature from the real space charge modulation amplitude imaged by scanning tunnelling microscopy. This study lifts the disagreement of previous independent transport measurements. We find that thickness can be a non-trivial tuning parameter and demonstrate the importance of considering a finite thickness range to accurately characterize its influence.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Isolating single unit-cell thin layers from the bulk matrix of layered compounds offers tremendous opportunities to design novel functional electronic materials. However, a comprehensive thickness dependence study is paramount to harness the electronic properties of such atomic foils and their stacking into synthetic heterostructures. Here we show that a dimensional crossover and quantum confinement with reducing thickness result in a striking non-monotonic evolution of the charge density wave transition temperature in VSe2. Our conclusion is drawn from a direct derivation of the local order parameter and transition temperature from the real space charge modulation amplitude imaged by scanning tunnelling microscopy. This study lifts the disagreement of previous independent transport measurements. We find that thickness can be a non-trivial tuning parameter and demonstrate the importance of considering a finite thickness range to accurately characterize its influence. | |
T. Jaouen; B. Hildebrand; M. L. Mottas; I. M. Di Giovannantonio; P. Ruffieux; M. Rumo; C. W. Nicholson; E. Razzoli; C. Barreteau; A. Ubaldini; E. Giannini; F. Vanini; H. Beck; C. Monney; P. Aebi Phase separation in the vicinity of Fermi surface hot spots Journal Article Physical Review B, 100 (7), pp. 075152, 2019. @article{Jaouen2019, title = {Phase separation in the vicinity of Fermi surface hot spots}, author = {T. Jaouen and B. Hildebrand and M. L. Mottas and I. M. Di Giovannantonio and P. Ruffieux and M. Rumo and C. W. Nicholson and E. Razzoli and C. Barreteau and A. Ubaldini and E. Giannini and F. Vanini and H. Beck and C. Monney and P. Aebi}, url = {https://link.aps.org/doi/10.1103/PhysRevB.100.075152}, doi = {10.1103/PhysRevB.100.075152}, year = {2019}, date = {2019-08-11}, journal = {Physical Review B}, volume = {100}, number = {7}, pages = {075152}, abstract = {Spatially inhomogeneous electronic states are expected to be key ingredients for the emergence of superconducting phases in quantum materials hosting charge-density waves (CDWs). Prototypical materials are transition-metal dichalcogenides (TMDCs) and among them, 1T−TiSe2 exhibiting intertwined CDW and superconducting states under Cu intercalation, pressure, or electrical gating. Although it has been recently proposed that the emergence of superconductivity relates to CDW fluctuations and the development of spatial inhomogeneities in the CDW order, the fundamental mechanism underlying such a phase separation (PS) is still missing. Using angle-resolved photoemission spectroscopy and variable-temperature scanning tunneling microscopy, we report on the phase diagram of the CDW in 1T−TiSe2 as a function of Ti self-doping, an overlooked degree of freedom inducing CDW texturing. We find an intrinsic tendency towards electronic PS in the vicinity of Fermi surface (FS) “hot spots,” i.e., locations with band crossings close to, but not at the Fermi level. We therefore demonstrate an intimate relationship between the FS topology and the emergence of spatially textured electronic phases which is expected to be generalizable to many doped CDW compounds.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Spatially inhomogeneous electronic states are expected to be key ingredients for the emergence of superconducting phases in quantum materials hosting charge-density waves (CDWs). Prototypical materials are transition-metal dichalcogenides (TMDCs) and among them, 1T−TiSe2 exhibiting intertwined CDW and superconducting states under Cu intercalation, pressure, or electrical gating. Although it has been recently proposed that the emergence of superconductivity relates to CDW fluctuations and the development of spatial inhomogeneities in the CDW order, the fundamental mechanism underlying such a phase separation (PS) is still missing. Using angle-resolved photoemission spectroscopy and variable-temperature scanning tunneling microscopy, we report on the phase diagram of the CDW in 1T−TiSe2 as a function of Ti self-doping, an overlooked degree of freedom inducing CDW texturing. We find an intrinsic tendency towards electronic PS in the vicinity of Fermi surface (FS) “hot spots,” i.e., locations with band crossings close to, but not at the Fermi level. We therefore demonstrate an intimate relationship between the FS topology and the emergence of spatially textured electronic phases which is expected to be generalizable to many doped CDW compounds. | |
D. van der Marel; F. Barantani; C. W. Rischau Possible mechanism for superconductivity in doped SrTiO3 Journal Article Physical Review Research, 1 (1), pp. 013003, 2019. @article{vanderMarel2019b, title = {Possible mechanism for superconductivity in doped SrTiO3}, author = {D. van der Marel and F. Barantani and C. W. Rischau}, url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.1.013003}, doi = {https://doi.org/10.1103/PhysRevResearch.1.013003}, year = {2019}, date = {2019-08-09}, journal = {Physical Review Research}, volume = {1}, number = {1}, pages = {013003}, abstract = {The soft ferroelectric phonon in SrTiO3 observed with optical spectroscopy has an extraordinarily strong spectral weight which is much stronger than expected in the limit of a perfectly ionic compound. This “charged phonon” effect in SrTiO3 is caused by the close-to-covalent character of the Ti-O ionic bond and implies a strong coupling between the soft ferroelectric phonon and the interband transitions across the 3-eV gap of SrTiO3. We demonstrate that this coupling leads, in addition to the charged phonon effect, to a pairing interaction involving the exchange of two transverse optical phonons. This process owes its relevance to the strong electron-phonon coupling and to the fact that the interaction mediated by a single transverse optical phonon vanishes at low electron density. We use the experimental soft phonon spectral weight to calculate the strength of the biphonon mediated pairing interaction in the electron-doped material and show that it is of the correct magnitude when compared to the experimental value of the superconducting critical temperature. Biphonon exchange is therefore an important pairing mechanism at low doping, and may be the key to understanding the occurrence of superconductivity in doped SrTiO3 and other low electron density materials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The soft ferroelectric phonon in SrTiO3 observed with optical spectroscopy has an extraordinarily strong spectral weight which is much stronger than expected in the limit of a perfectly ionic compound. This “charged phonon” effect in SrTiO3 is caused by the close-to-covalent character of the Ti-O ionic bond and implies a strong coupling between the soft ferroelectric phonon and the interband transitions across the 3-eV gap of SrTiO3. We demonstrate that this coupling leads, in addition to the charged phonon effect, to a pairing interaction involving the exchange of two transverse optical phonons. This process owes its relevance to the strong electron-phonon coupling and to the fact that the interaction mediated by a single transverse optical phonon vanishes at low electron density. We use the experimental soft phonon spectral weight to calculate the strength of the biphonon mediated pairing interaction in the electron-doped material and show that it is of the correct magnitude when compared to the experimental value of the superconducting critical temperature. Biphonon exchange is therefore an important pairing mechanism at low doping, and may be the key to understanding the occurrence of superconductivity in doped SrTiO3 and other low electron density materials. | |
Ievgeniia O Nedoliuk; Sheng Hu; Andre K Geim; Alexey B Kuzmenko Colossal infrared and terahertz magneto-optical activity in a two-dimensional Dirac material Journal Article NATURE NANOTECHNOLOGY, 14 (8), pp. 756-761, 2019, ISSN: 1748-3387. @article{ISI:000478794700014, title = {Colossal infrared and terahertz magneto-optical activity in a two-dimensional Dirac material}, author = {Ievgeniia O Nedoliuk and Sheng Hu and Andre K Geim and Alexey B Kuzmenko}, doi = {10.1038/s41565-019-0489-8}, issn = {1748-3387}, year = {2019}, date = {2019-08-01}, journal = {NATURE NANOTECHNOLOGY}, volume = {14}, number = {8}, pages = {756-761}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {When two-dimensional electron gases (2DEGs) are exposed to a magnetic field, they resonantly absorb electromagnetic radiation via electronic transitions between Landau levels(1). In 2DEGs with a Dirac spectrum, such as graphene, theory predicts an exceptionally high infrared magneto-absorption, even at zero doping(2-5). However, the measured Landau-level magneto-optical effects in graphene have been much weaker than expected(2,6-12) because of imperfections in the samples available for such experiments. Here, we measure magneto-transmission and Faraday rotation in high-mobility encapsulated monolayer graphene using a custom-designed set-up for magneto-infrared microspectroscopy. Our results show strongly enhanced magneto-optical activity in the infrared and terahertz ranges, characterized by absorption of light near to the 50% maximum allowed, 100% magnetic circular dichroism and high Faraday rotation. Considering that sizeable effects have been already observed at routinely achievable magnetic fields, our findings demonstrate the potential of magnetic tuning in 2D Dirac materials for long-wavelength optoelectronics and plasmonics.}, keywords = {}, pubstate = {published}, tppubtype = {article} } When two-dimensional electron gases (2DEGs) are exposed to a magnetic field, they resonantly absorb electromagnetic radiation via electronic transitions between Landau levels(1). In 2DEGs with a Dirac spectrum, such as graphene, theory predicts an exceptionally high infrared magneto-absorption, even at zero doping(2-5). However, the measured Landau-level magneto-optical effects in graphene have been much weaker than expected(2,6-12) because of imperfections in the samples available for such experiments. Here, we measure magneto-transmission and Faraday rotation in high-mobility encapsulated monolayer graphene using a custom-designed set-up for magneto-infrared microspectroscopy. Our results show strongly enhanced magneto-optical activity in the infrared and terahertz ranges, characterized by absorption of light near to the 50% maximum allowed, 100% magnetic circular dichroism and high Faraday rotation. Considering that sizeable effects have been already observed at routinely achievable magnetic fields, our findings demonstrate the potential of magnetic tuning in 2D Dirac materials for long-wavelength optoelectronics and plasmonics. | |
W Luo; M. Boselli; J M Poumirol; I Ardizzone; J Teyssier; D van der Marel; S Gariglio; J M Triscone; A B Kuzmenko High sensitivity variable-temperature infrared nanoscopy of conducting oxide interfaces Journal Article Nature Communications, 10 (1), pp. 2774, 2019. @article{Luo2019, title = {High sensitivity variable-temperature infrared nanoscopy of conducting oxide interfaces}, author = {W Luo and M. Boselli and J M Poumirol and I Ardizzone and J Teyssier and D van der Marel and S Gariglio and J M Triscone and A B Kuzmenko}, url = {https://doi.org/10.1038/s41467-019-10672-5}, doi = {10.1038/s41467-019-10672-5}, year = {2019}, date = {2019-06-24}, journal = {Nature Communications}, volume = {10}, number = {1}, pages = {2774}, abstract = {Probing the local transport properties of two-dimensional electron systems (2DES) confined at buried interfaces requires a non-invasive technique with a high spatial resolution operating in a broad temperature range. In this paper, we investigate the scattering-type scanning near field optical microscopy as a tool for studying the conducting LaAlO3/SrTiO3 interface from room temperature down to 6 K. We show that the near-field optical signal, in particular its phase component, is highly sensitive to the transport properties of the electron system present at the interface. Our modeling reveals that such sensitivity originates from the interaction of the AFM tip with coupled plasmon–phonon modes with a small penetration depth. The model allows us to quantitatively correlate changes in the optical signal with the variation of the 2DES transport properties induced by cooling and by electrostatic gating. To probe the spatial resolution of the technique, we image conducting nano-channels written in insulating heterostructures with a voltage-biased tip of an atomic force microscope.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Probing the local transport properties of two-dimensional electron systems (2DES) confined at buried interfaces requires a non-invasive technique with a high spatial resolution operating in a broad temperature range. In this paper, we investigate the scattering-type scanning near field optical microscopy as a tool for studying the conducting LaAlO3/SrTiO3 interface from room temperature down to 6 K. We show that the near-field optical signal, in particular its phase component, is highly sensitive to the transport properties of the electron system present at the interface. Our modeling reveals that such sensitivity originates from the interaction of the AFM tip with coupled plasmon–phonon modes with a small penetration depth. The model allows us to quantitatively correlate changes in the optical signal with the variation of the 2DES transport properties induced by cooling and by electrostatic gating. To probe the spatial resolution of the technique, we image conducting nano-channels written in insulating heterostructures with a voltage-biased tip of an atomic force microscope. | |
L. Thiel; Z. Wang; M. A. Tschudin; D. Rohner; I. Gutierrez-Lezama; N. Ubrig; M. Gibertini; E. Giannini; A. F. Morpurgo; P. Maletinsky Probing magnetism in 2D materials at the nanoscale with single-spin microscopy Journal Article Science, 364 (6444), pp. 973-976, 2019. @article{Thiel2019, title = {Probing magnetism in 2D materials at the nanoscale with single-spin microscopy}, author = {L. Thiel and Z. Wang and M. A. Tschudin and D. Rohner and I. Gutierrez-Lezama and N. Ubrig and M. Gibertini and E. Giannini and A. F. Morpurgo and P. Maletinsky}, url = {https://science.sciencemag.org/content/364/6444/973}, doi = {10.1126/science.aav6926}, year = {2019}, date = {2019-06-07}, journal = {Science}, volume = {364}, number = {6444}, pages = {973-976}, abstract = {The discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) crystals has generated widespread interest. Making further progress in this area requires quantitative knowledge of the magnetic properties of vdW magnets at the nanoscale. We used scanning single-spin magnetometry based on diamond nitrogen-vacancy centers to image the magnetization, localized defects, and magnetic domains of atomically thin crystals of the vdW magnet chromium(III) iodide (CrI3). We determined the magnetization of CrI3 monolayers to be ≈16 Bohr magnetons per square nanometer, with comparable values in samples with odd numbers of layers; however, the magnetization vanishes when the number of layers is even. We also found that structural modifications can induce switching between ferromagnetic and antiferromagnetic interlayer ordering. These results demonstrate the benefit of using single-spin scanning magnetometry to study the magnetism of 2D vdW magnets.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The discovery of ferromagnetism in two-dimensional (2D) van der Waals (vdW) crystals has generated widespread interest. Making further progress in this area requires quantitative knowledge of the magnetic properties of vdW magnets at the nanoscale. We used scanning single-spin magnetometry based on diamond nitrogen-vacancy centers to image the magnetization, localized defects, and magnetic domains of atomically thin crystals of the vdW magnet chromium(III) iodide (CrI3). We determined the magnetization of CrI3 monolayers to be ≈16 Bohr magnetons per square nanometer, with comparable values in samples with odd numbers of layers; however, the magnetization vanishes when the number of layers is even. We also found that structural modifications can induce switching between ferromagnetic and antiferromagnetic interlayer ordering. These results demonstrate the benefit of using single-spin scanning magnetometry to study the magnetism of 2D vdW magnets. | |
M. Spera; A. Scarfato; E. Giannini; C. Renner Energy-dependent spatial texturing of charge order in 1T-CuxTiSe2 Journal Article Physical Review B, 99 (15), pp. 155133, 2019. @article{Spera2019, title = {Energy-dependent spatial texturing of charge order in 1T-CuxTiSe2}, author = {M. Spera and A. Scarfato and E. Giannini and C. Renner}, year = {2019}, date = {2019-04-18}, journal = {Physical Review B}, volume = {99}, number = {15}, pages = {155133}, abstract = {We report a detailed study of the microscopic effects of Cu intercalation on the charge density wave (CDW) in 1T−CuxTiSe2. Scanning tunneling microscopy and spectroscopy reveal a unique, Cu-driven spatial texturing of the charge-ordered phase, with the appearance of energy-dependent CDW patches and sharp π-phase shift domain walls (πDWs). The energy and doping dependencies of the patchwork are directly linked to the inhomogeneous potential landscape due to the Cu intercalants. They imply a CDW gap with unusual features, including a large amplitude, the opening below the Fermi level, and a shift to higher binding energy with electron doping. Unlike the patchwork, the πDWs occur independently of the intercalated Cu distribution. They remain atomically sharp throughout the investigated phase diagram and occur in both superconducting and nonsuperconducting specimens. These results provide unique atomic-scale insight into the CDW ground state, questioning the existence of incommensurate CDW domain walls and contributing to understanding its formation mechanism and interplay with superconductivity.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report a detailed study of the microscopic effects of Cu intercalation on the charge density wave (CDW) in 1T−CuxTiSe2. Scanning tunneling microscopy and spectroscopy reveal a unique, Cu-driven spatial texturing of the charge-ordered phase, with the appearance of energy-dependent CDW patches and sharp π-phase shift domain walls (πDWs). The energy and doping dependencies of the patchwork are directly linked to the inhomogeneous potential landscape due to the Cu intercalants. They imply a CDW gap with unusual features, including a large amplitude, the opening below the Fermi level, and a shift to higher binding energy with electron doping. Unlike the patchwork, the πDWs occur independently of the intercalated Cu distribution. They remain atomically sharp throughout the investigated phase diagram and occur in both superconducting and nonsuperconducting specimens. These results provide unique atomic-scale insight into the CDW ground state, questioning the existence of incommensurate CDW domain walls and contributing to understanding its formation mechanism and interplay with superconductivity. | |
M.-L. Mottas; T. Jaouen; B. Hildebrand; M. Rumo; F. Vanini; E. Razzoli; E. Giannini; C. Barreteau; D. R. Bowler; C. Monney; H. Beck; and P. Aebi Semimetal-to-semiconductor transition and charge-density-wave suppression in 1T−TiSe2−xSx single crystals Journal Article Physical Review B, 99 (15), pp. 155103, 2019. @article{Mottas2019, title = {Semimetal-to-semiconductor transition and charge-density-wave suppression in 1T−TiSe2−xSx single crystals}, author = {M.-L. Mottas and T. Jaouen and B. Hildebrand and M. Rumo and F. Vanini and E. Razzoli and E. Giannini and C. Barreteau and D. R. Bowler and C. Monney and H. Beck and and P. Aebi}, url = {https://link.aps.org/doi/10.1103/PhysRevB.99.155103}, doi = {10.1103/PhysRevB.99.155103}, year = {2019}, date = {2019-04-01}, journal = {Physical Review B}, volume = {99}, number = {15}, pages = {155103}, abstract = {The transition-metal dichalcogenide 1T−TiSe2 is a quasi-two-dimensional layered material with a phase transition towards a commensurate charge-density wave (CDW) at a critical temperature Tc≈200K. The relationship between the origin of the CDW instability and the semimetallic or semiconducting character of the normal state, i.e., with the nonreconstructed Fermi-surface topology, remains elusive. By combining angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations, we investigate 1T−TiSe2−xSx single crystals. Using STM, we first show that the long-range phase-coherent CDW state is stable against S substitutions with concentrations, at least, up to x=0.34. The ARPES measurements then reveal a slow but continuous decrease in the overlap between the electron and the hole (e−h) bands of the semimetallic normal state well reproduced by DFT and related to slight reductions of both the CDW order parameter and Tc. Our DFT calculations further predict a semimetal-to-semiconductor transition of the normal state at a higher critical S concentration of xc=0.9±0.1 that coincides with a suppressed CDW state in TiSeS as measured with STM. Finally, we rationalize the x dependence of the e−h band overlap in terms of isovalent substitution-induced competing chemical pressure and charge localization effects. Our study highlights the key role of the e−h band overlap for the CDW instability.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The transition-metal dichalcogenide 1T−TiSe2 is a quasi-two-dimensional layered material with a phase transition towards a commensurate charge-density wave (CDW) at a critical temperature Tc≈200K. The relationship between the origin of the CDW instability and the semimetallic or semiconducting character of the normal state, i.e., with the nonreconstructed Fermi-surface topology, remains elusive. By combining angle-resolved photoemission spectroscopy (ARPES), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations, we investigate 1T−TiSe2−xSx single crystals. Using STM, we first show that the long-range phase-coherent CDW state is stable against S substitutions with concentrations, at least, up to x=0.34. The ARPES measurements then reveal a slow but continuous decrease in the overlap between the electron and the hole (e−h) bands of the semimetallic normal state well reproduced by DFT and related to slight reductions of both the CDW order parameter and Tc. Our DFT calculations further predict a semimetal-to-semiconductor transition of the normal state at a higher critical S concentration of xc=0.9±0.1 that coincides with a suppressed CDW state in TiSeS as measured with STM. Finally, we rationalize the x dependence of the e−h band overlap in terms of isovalent substitution-induced competing chemical pressure and charge localization effects. Our study highlights the key role of the e−h band overlap for the CDW instability. | |
O. Shcherban; L. Akselrud; E. Giannini; R. Gladyshevskii Refinement of the Modulated Structures of Pb-Free and Pb-Doped Bi-2223 HTSC Journal Article Acta Physica Polonica A, 133 (4), pp. 1027-1029, 2019. @article{Shcherban2019, title = {Refinement of the Modulated Structures of Pb-Free and Pb-Doped Bi-2223 HTSC}, author = {O. Shcherban and L. Akselrud and E. Giannini and R. Gladyshevskii}, url = {http://psjd.icm.edu.pl/psjd/element/bwmeta1.element.bwnjournal-article-appv133n4p62kz}, year = {2019}, date = {2019-04-01}, journal = {Acta Physica Polonica A}, volume = {133}, number = {4}, pages = {1027-1029}, abstract = {The incommensurate modulated structures of Pb-free and Pb-doped Bi-2223 phases were refined on single-crystal X-ray diffraction data. }, keywords = {}, pubstate = {published}, tppubtype = {article} } The incommensurate modulated structures of Pb-free and Pb-doped Bi-2223 phases were refined on single-crystal X-ray diffraction data. | |
Dirk van der Marel Time to respond (Commentary) Online Journal Club for Condensed Matter Physics 2019. @online{vanderMarel2019, title = {Time to respond (Commentary)}, author = {Dirk van der Marel}, url = {https://www.condmatjclub.org/uploads/2019/01/JCCM_January_2019_01.pdf}, year = {2019}, date = {2019-01-01}, organization = {Journal Club for Condensed Matter Physics}, abstract = {Dirk van der Marel writes on some fascinating new technical developments on wideband spectroscopy far far below the diffraction limit and developments following from it including transient spectroscopy.}, keywords = {}, pubstate = {published}, tppubtype = {online} } Dirk van der Marel writes on some fascinating new technical developments on wideband spectroscopy far far below the diffraction limit and developments following from it including transient spectroscopy. | |
I. Cucchi; I. Gutierrez-Lezama; E. Cappelli; S. M. Walker; F. Y. Bruno; G. Tenasini; L. Wang; N. Ubrig; C. Barreteau; E. Giannini; M. Gibertini; A. Tamai; A. F. Morpurgo; F. Baumberger Microfocus Laser–Angle-Resolved Photoemission on Encapsulated Mono-, Bi-, and Few-Layer 1T′-WTe2 Journal Article Nano Letters, 19 (1), pp. 554-560, 2018. @article{Cucchi2018, title = {Microfocus Laser–Angle-Resolved Photoemission on Encapsulated Mono-, Bi-, and Few-Layer 1T′-WTe2}, author = {I. Cucchi and I. Gutierrez-Lezama and E. Cappelli and S. M. Walker and F. Y. Bruno and G. Tenasini and L. Wang and N. Ubrig and C. Barreteau and E. Giannini and M. Gibertini and A. Tamai and A. F. Morpurgo and F. Baumberger}, doi = {https://doi.org/10.1021/acs.nanolett.8b04534}, year = {2018}, date = {2018-12-20}, journal = {Nano Letters}, volume = {19}, number = {1}, pages = {554-560}, abstract = {Two-dimensional crystals of semi-metallic van der Waals materials hold much potential for the realization of novel phases, as exemplified by the recent discoveries of a polar metal in few-layer 1T′-WTe2 and of a quantum spin Hall state in monolayers of the same material. Understanding these phases is particularly challenging because little is known from experiments about the momentum space electronic structure of ultrathin crystals. Here, we report direct electronic structure measurements of exfoliated mono-, bi-, and few-layer 1T′-WTe2 by laser-based microfocus angle-resolved photoemission. This is achieved by encapsulating with monolayer graphene a flake of WTe2 comprising regions of different thickness. Our data support the recent identification of a quantum spin Hall state in monolayer 1T′-WTe2 and reveal strong signatures of the broken inversion symmetry in the bilayer. We finally discuss the sensitivity of encapsulated samples to contaminants following exposure to ambient atmosphere.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Two-dimensional crystals of semi-metallic van der Waals materials hold much potential for the realization of novel phases, as exemplified by the recent discoveries of a polar metal in few-layer 1T′-WTe2 and of a quantum spin Hall state in monolayers of the same material. Understanding these phases is particularly challenging because little is known from experiments about the momentum space electronic structure of ultrathin crystals. Here, we report direct electronic structure measurements of exfoliated mono-, bi-, and few-layer 1T′-WTe2 by laser-based microfocus angle-resolved photoemission. This is achieved by encapsulating with monolayer graphene a flake of WTe2 comprising regions of different thickness. Our data support the recent identification of a quantum spin Hall state in monolayer 1T′-WTe2 and reveal strong signatures of the broken inversion symmetry in the bilayer. We finally discuss the sensitivity of encapsulated samples to contaminants following exposure to ambient atmosphere. | |
S Borroni; J Teyssier; P Piekarz; A B Kuzmenko; A M Oleifmmode acuteselse śfi; J Lorenzana; F Carbone Light scattering from the critical modes of the Verwey transition in magnetite Journal Article Phys. Rev. B, 98 , pp. 184301, 2018. @article{PhysRevB.98.184301, title = {Light scattering from the critical modes of the Verwey transition in magnetite}, author = {S Borroni and J Teyssier and P Piekarz and A B Kuzmenko and A M Oleifmmode acute{s}else śfi{} and J Lorenzana and F Carbone}, url = {https://link.aps.org/doi/10.1103/PhysRevB.98.184301}, doi = {10.1103/PhysRevB.98.184301}, year = {2018}, date = {2018-11-01}, journal = {Phys. Rev. B}, volume = {98}, pages = {184301}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Alsu Gazizulina; Diana Lucia Quintero-Castro; Dirk Wulferding; Jeremie Teyssier; Karel Prokes; Fabiano Yokaichiya; Andreas Schilling Tuning the orbital-lattice fluctuations in the mixed spin-dimer system Ba3-xSrxCr2O8 Journal Article Phys. Rev. B, 98 , pp. 144115, 2018. @article{PhysRevB.98.144115, title = {Tuning the orbital-lattice fluctuations in the mixed spin-dimer system Ba3-xSrxCr2O8}, author = {Alsu Gazizulina and Diana Lucia Quintero-Castro and Dirk Wulferding and Jeremie Teyssier and Karel Prokes and Fabiano Yokaichiya and Andreas Schilling}, url = {https://link.aps.org/doi/10.1103/PhysRevB.98.144115}, doi = {10.1103/PhysRevB.98.144115}, year = {2018}, date = {2018-10-01}, journal = {Phys. Rev. B}, volume = {98}, pages = {144115}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
K Wang; N Bachar; J Teyssier; W Luo; C W Rischau; G Scheerer; A de la Torre; R S Perry; F Baumberger; D van der Marel Mott transition and collective charge pinning in electron doped Sr2IrO4 Journal Article Phys. Rev. B, 98 , pp. 045107, 2018. @article{PhysRevB.98.045107, title = {Mott transition and collective charge pinning in electron doped Sr2IrO4}, author = {K Wang and N Bachar and J Teyssier and W Luo and C W Rischau and G Scheerer and A de la Torre and R S Perry and F Baumberger and D van der Marel}, url = {https://link.aps.org/doi/10.1103/PhysRevB.98.045107}, doi = {10.1103/PhysRevB.98.045107}, year = {2018}, date = {2018-07-01}, journal = {Phys. Rev. B}, volume = {98}, pages = {045107}, publisher = {American Physical Society}, abstract = {We studied the in-plane dynamic and static charge conductivity of electron doped Sr2IrO4 using optical spectroscopy and DC transport measurements. The optical conductivity indicates that the pristine material is an indirect semiconductor with a direct Mott gap of 0.55 eV. Upon substitution of 2% La per formula unit the Mott gap is suppressed except in a small fraction of the material (15%) where the gap survives, and overall the material remains insulating. Instead of a zero energy mode (or Drude peak) we observe a soft collective mode (SCM) with a broad maximum at 40meV. Doping to 10% increases the strength of the SCM, and a zero-energy mode occurs together with metallic DC conductivity. Further increase of the La substitution doesn't change the spectral weight integral up to 3 eV. It does however result in a transfer of the SCM spectral weight to the zero-energy mode, with a corresponding reduction of the DC resistivity for all temperatures from 4 to 300 K. The presence of a zero-energy mode signals that at least part of the Fermi surface remains ungapped at low temperatures, whereas the SCM appears to be caused by pinning a collective frozen state involving part of the doped electrons.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We studied the in-plane dynamic and static charge conductivity of electron doped Sr2IrO4 using optical spectroscopy and DC transport measurements. The optical conductivity indicates that the pristine material is an indirect semiconductor with a direct Mott gap of 0.55 eV. Upon substitution of 2% La per formula unit the Mott gap is suppressed except in a small fraction of the material (15%) where the gap survives, and overall the material remains insulating. Instead of a zero energy mode (or Drude peak) we observe a soft collective mode (SCM) with a broad maximum at 40meV. Doping to 10% increases the strength of the SCM, and a zero-energy mode occurs together with metallic DC conductivity. Further increase of the La substitution doesn't change the spectral weight integral up to 3 eV. It does however result in a transfer of the SCM spectral weight to the zero-energy mode, with a corresponding reduction of the DC resistivity for all temperatures from 4 to 300 K. The presence of a zero-energy mode signals that at least part of the Fermi surface remains ungapped at low temperatures, whereas the SCM appears to be caused by pinning a collective frozen state involving part of the doped electrons. | |
Z. Wang; I. Gutiérrez-Lezama; N. Ubrig; M. Kroner; M. Gibertini; T. Taniguchi; K. Watanabe; A. Imamoğlu; E. Giannini; A. F. Morpurgo Very large tunneling magnetoresistance in layered magnetic semiconductor CrI3 Journal Article Nature Communications, 9 (1), pp. 2516, 2018. @article{Wang2018, title = {Very large tunneling magnetoresistance in layered magnetic semiconductor CrI3}, author = {Z. Wang and I. Gutiérrez-Lezama and N. Ubrig and M. Kroner and M. Gibertini and T. Taniguchi and K. Watanabe and A. Imamoğlu and E. Giannini and A. F. Morpurgo}, doi = {10.1038/s41467-018-04953-8}, year = {2018}, date = {2018-06-28}, journal = {Nature Communications}, volume = {9}, number = {1}, pages = {2516}, abstract = {Magnetic layered van der Waals crystals are an emerging class of materials giving access to new physical phenomena, as illustrated by the recent observation of 2D ferromagnetism in Cr2Ge2Te6 and CrI3. Of particular interest in semiconductors is the interplay between magnetism and transport, which has remained unexplored. Here we report magneto-transport measurements on exfoliated CrI3 crystals. We find that tunneling conduction in the direction perpendicular to the crystalline planes exhibits a magnetoresistance as large as 10,000%. The evolution of the magnetoresistance with magnetic field and temperature reveals that the phenomenon originates from multiple transitions to different magnetic states, whose possible microscopic nature is discussed on the basis of all existing experimental observations. This observed dependence of the conductance of a tunnel barrier on its magnetic state is a phenomenon that demonstrates the presence of a strong coupling between transport and magnetism in magnetic van der Waals semiconductors.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Magnetic layered van der Waals crystals are an emerging class of materials giving access to new physical phenomena, as illustrated by the recent observation of 2D ferromagnetism in Cr2Ge2Te6 and CrI3. Of particular interest in semiconductors is the interplay between magnetism and transport, which has remained unexplored. Here we report magneto-transport measurements on exfoliated CrI3 crystals. We find that tunneling conduction in the direction perpendicular to the crystalline planes exhibits a magnetoresistance as large as 10,000%. The evolution of the magnetoresistance with magnetic field and temperature reveals that the phenomenon originates from multiple transitions to different magnetic states, whose possible microscopic nature is discussed on the basis of all existing experimental observations. This observed dependence of the conductance of a tunnel barrier on its magnetic state is a phenomenon that demonstrates the presence of a strong coupling between transport and magnetism in magnetic van der Waals semiconductors. | |
Tamagnone Michele; Slipchenko Tetiana M.; Moldovan Clara; Liu Peter Q.; Centeno Alba; Hasani Hamed; Zurutuza Amaia; Ionescu Adrian M.; Martin-Moreno Luis; Faist Jérôme; Mosig Juan R.; Kuzmenko Alexey B.; Poumirol Jean-Marie Magnetoplasmonic enhancement of Faraday rotation in patterned graphene metasurfaces Journal Article Phys. Rev. B, 97 (24), pp. 241410, 2018. @article{Michele2018, title = {Magnetoplasmonic enhancement of Faraday rotation in patterned graphene metasurfaces}, author = {Tamagnone Michele and Slipchenko Tetiana M. and Moldovan Clara and Liu Peter Q. and Centeno Alba and Hasani Hamed and Zurutuza Amaia and Ionescu Adrian M. and Martin-Moreno Luis and Faist Jérôme and Mosig Juan R. and Kuzmenko Alexey B. and Poumirol Jean-Marie}, url = {https://link.aps.org/doi/10.1103/PhysRevB.97.241410}, doi = {10.1103/PhysRevB.97.241410}, year = {2018}, date = {2018-06-26}, journal = {Phys. Rev. B}, volume = {97}, number = {24}, pages = {241410}, abstract = {Faraday rotation is a fundamental property present in all nonreciprocal optical elements. In the THz range, graphene displays strong Faraday rotation; unfortunately, it is limited to frequencies below the cyclotron resonance. Here, we show experimentally that in specifically designed metasurfaces, magnetoplasmons can be used to circumvent this limitation. We find excellent agreement between theory and experiment and provide physical insights and predictions on these phenomena. Finally, we demonstrate strong tunability in these metasurfaces using electric and magnetic field biasing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Faraday rotation is a fundamental property present in all nonreciprocal optical elements. In the THz range, graphene displays strong Faraday rotation; unfortunately, it is limited to frequencies below the cyclotron resonance. Here, we show experimentally that in specifically designed metasurfaces, magnetoplasmons can be used to circumvent this limitation. We find excellent agreement between theory and experiment and provide physical insights and predictions on these phenomena. Finally, we demonstrate strong tunability in these metasurfaces using electric and magnetic field biasing. | |
Liang Yang; Jing Tian; Henry Giddens; Jean-Marie Poumirol; JingBo Wu; Alexey B. Kuzmenko; Yang Hao Magnetically tunable graphene-based reflector under linear polarized incidence at room temperature Journal Article Applied Physics Letters, 112 (15), pp. 151103, 2018. @article{Yang2018, title = {Magnetically tunable graphene-based reflector under linear polarized incidence at room temperature}, author = {Liang Yang and Jing Tian and Henry Giddens and Jean-Marie Poumirol and JingBo Wu and Alexey B. Kuzmenko and Yang Hao}, url = {https://aip.scitation.org/doi/abs/10.1063/1.5022774}, doi = {10.1063/1.5022774}, year = {2018}, date = {2018-06-13}, journal = {Applied Physics Letters}, volume = {112}, number = {15}, pages = {151103}, abstract = {At the terahertz spectrum, the 2D material graphene has diagonal and Hall conductivities in the presence of a magnetic field. These peculiar properties provide graphene-based structures with a magnetically tunable response to electromagnetic waves. In this work, the absolute reflection intensity was measured for a graphene-based reflector illuminated by linearly polarized incident waves at room temperature, which demonstrated the intensity modulation depth (IMD) under different magnetostatic biases by up to 15%. Experimental data were fitted and analyzed by a modified equivalent circuit model. In addition, as an important phenomenon of the graphene gyrotropic response, Kerr rotation is discussed according to results achieved from full-wave simulations. It is concluded that the IMD is reduced for the best Kerr rotation in the proposed graphene-based reflector.}, keywords = {}, pubstate = {published}, tppubtype = {article} } At the terahertz spectrum, the 2D material graphene has diagonal and Hall conductivities in the presence of a magnetic field. These peculiar properties provide graphene-based structures with a magnetically tunable response to electromagnetic waves. In this work, the absolute reflection intensity was measured for a graphene-based reflector illuminated by linearly polarized incident waves at room temperature, which demonstrated the intensity modulation depth (IMD) under different magnetostatic biases by up to 15%. Experimental data were fitted and analyzed by a modified equivalent circuit model. In addition, as an important phenomenon of the graphene gyrotropic response, Kerr rotation is discussed according to results achieved from full-wave simulations. It is concluded that the IMD is reduced for the best Kerr rotation in the proposed graphene-based reflector. | |
D. Matera; M. Bonura; C. Barth; A. Fete; R. Černý; E. Giannini; C. Senatore Rapid synthesis of MgB2 by inductive heating Journal Article IEEE Transactions on Applied Superconductivity, 28 (4), pp. 1-5, 2018. @article{Matera2018, title = {Rapid synthesis of MgB2 by inductive heating}, author = {D. Matera and M. Bonura and C. Barth and A. Fete and R. Černý and E. Giannini and C. Senatore}, doi = {10.1109/TASC.2018.2798299}, year = {2018}, date = {2018-06-10}, journal = {IEEE Transactions on Applied Superconductivity}, volume = {28}, number = {4}, pages = {1-5}, abstract = {The effect of a rapid internal magnesium diffusion synthesis on the electrical, magnetic, and microstructural properties of binary MgB 2 bulk samples has been investigated. We have used a laboratory-made induction furnace to reduce the reaction time, typically of many hours, to few minutes. We report a comparison between two samples reacted at the same temperature with the induction furnace and with a commercial resistance oven. We have observed that the critical temperature and the width of the superconducting transition are not affected by the heat treatment. The induction heating leads to an increase of the critical current density at high fields, correlated with an enhancement of the upper critical field. This paper exposes the potentiality of the proposed fast process, which allows tuning the parameters of the heat treatment in ranges that would not be accessible with traditional ovens. The technique can be scaled for the preparation of wires and powders.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effect of a rapid internal magnesium diffusion synthesis on the electrical, magnetic, and microstructural properties of binary MgB 2 bulk samples has been investigated. We have used a laboratory-made induction furnace to reduce the reaction time, typically of many hours, to few minutes. We report a comparison between two samples reacted at the same temperature with the induction furnace and with a commercial resistance oven. We have observed that the critical temperature and the width of the superconducting transition are not affected by the heat treatment. The induction heating leads to an increase of the critical current density at high fields, correlated with an enhancement of the upper critical field. This paper exposes the potentiality of the proposed fast process, which allows tuning the parameters of the heat treatment in ranges that would not be accessible with traditional ovens. The technique can be scaled for the preparation of wires and powders. | |
B. Hildebrand, T. Jaouen, M.-L. Mottas, G. Monney, C. Barreteau, E. Giannini, D. R. Bowler, P. Aebi: “”, Local Real-Space View of the Achiral 1T-TiSe2 2 x 2 x 2 Charge Density Wave Journal Article Physical Review Letters, 120 (13), pp. 136404, 2018. @article{Hildebrand2018, title = {Local Real-Space View of the Achiral 1T-TiSe2 2 x 2 x 2 Charge Density Wave}, author = {B. Hildebrand, T. Jaouen, M.-L. Mottas, G. Monney, C. Barreteau, E. Giannini, D. R. Bowler, P. Aebi: “”,}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.136404}, doi = {10.1103/PhysRevLett.120.136404}, year = {2018}, date = {2018-03-30}, journal = {Physical Review Letters}, volume = {120}, number = {13}, pages = {136404}, abstract = {The transition metal dichalcogenide 1T−TiSe2-two-dimensional layered material undergoing a commensurate 2×2×2 charge density wave (CDW) transition with a weak periodic lattice distortion (PLD) below ≈200 K. Scanning tunneling microscopy (STM) combined with intentionally introduced interstitial Ti atoms allows us to go beyond the usual spatial resolution of STM and to intimately probe the three-dimensional character of the PLD. Furthermore, the inversion-symmetric achiral nature of the CDW in the z direction is revealed, contradicting the claimed existence of helical CDW stacking and associated chiral order. This study paves the way to a simultaneous real-space probing of both charge and structural reconstructions in CDW compounds}, keywords = {}, pubstate = {published}, tppubtype = {article} } The transition metal dichalcogenide 1T−TiSe2-two-dimensional layered material undergoing a commensurate 2×2×2 charge density wave (CDW) transition with a weak periodic lattice distortion (PLD) below ≈200 K. Scanning tunneling microscopy (STM) combined with intentionally introduced interstitial Ti atoms allows us to go beyond the usual spatial resolution of STM and to intimately probe the three-dimensional character of the PLD. Furthermore, the inversion-symmetric achiral nature of the CDW in the z direction is revealed, contradicting the claimed existence of helical CDW stacking and associated chiral order. This study paves the way to a simultaneous real-space probing of both charge and structural reconstructions in CDW compounds | |
G Gäumann; I Crassee; N Numan; M Tamagnone; J R Mosig; J-M Poumirol; J-P Wolf; T Feurer Nonlinear THz spectroscopy and simulation of gated graphene Journal Article Journal of Physics Communications, 2 (6), pp. 065016, 2018. @article{2399-6528-2-6-065016, title = {Nonlinear THz spectroscopy and simulation of gated graphene}, author = {G Gäumann and I Crassee and N Numan and M Tamagnone and J R Mosig and J-M Poumirol and J-P Wolf and T Feurer}, url = {http://stacks.iop.org/2399-6528/2/i=6/a=065016}, year = {2018}, date = {2018-01-01}, journal = {Journal of Physics Communications}, volume = {2}, number = {6}, pages = {065016}, abstract = {We studied the nonlinear optical properties of single layer graphene using high terahertz (THz) fields. With the use of a back gate and cooling down the sample to cryogenic temperatures we are able to spectrally probe the nonlinear THz properties of intrinsic to highly doped graphene. The carrier density strongly affects the nonlinear properties of graphene; in the low doping and high THz field regime, an increase of the transmission on the order of 4% is found in our experiments. At higher doping levels we observe a larger relative nonlinear response: the larger the doping in the single layer the larger the relative field induced increase in transmission becomes. In all experiments, the THz field is opposing the effect of the gate, but field effects are never larger than the doping effects. We use the thermodynamical model for a hot electron gas also used by Mics et al (2015 Nat. Commun. 6 7655) to simulate our data and study the effects of doping on the nonlinear properties of single layer graphene. We find that the highest carrier temperatures are obtained in low doped graphene. The model shows a good qualitative agreement with our data for high doping levels. Nevertheless our results demonstrate the limitation of the model for low doping levels. Our results are a road map for further explorations for the control of nonlinear light–matter interaction and functionalization of graphene layers in active THz devices in which carrier temperature and saturable absorption play a role.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We studied the nonlinear optical properties of single layer graphene using high terahertz (THz) fields. With the use of a back gate and cooling down the sample to cryogenic temperatures we are able to spectrally probe the nonlinear THz properties of intrinsic to highly doped graphene. The carrier density strongly affects the nonlinear properties of graphene; in the low doping and high THz field regime, an increase of the transmission on the order of 4% is found in our experiments. At higher doping levels we observe a larger relative nonlinear response: the larger the doping in the single layer the larger the relative field induced increase in transmission becomes. In all experiments, the THz field is opposing the effect of the gate, but field effects are never larger than the doping effects. We use the thermodynamical model for a hot electron gas also used by Mics et al (2015 Nat. Commun. 6 7655) to simulate our data and study the effects of doping on the nonlinear properties of single layer graphene. We find that the highest carrier temperatures are obtained in low doped graphene. The model shows a good qualitative agreement with our data for high doping levels. Nevertheless our results demonstrate the limitation of the model for low doping levels. Our results are a road map for further explorations for the control of nonlinear light–matter interaction and functionalization of graphene layers in active THz devices in which carrier temperature and saturable absorption play a role. | |
D. van der Marel Order on command Journal Article Physics, 10 (127), 2017. @article{vanderMarel2017, title = {Order on command}, author = {D. van der Marel}, url = {https://physics.aps.org/articles/v10/127}, doi = {10.1103/Physics.10.127}, year = {2017}, date = {2017-11-27}, journal = {Physics}, volume = {10}, number = {127}, abstract = {A current of electrons with aligned spins can be used to modify magnetic order and superconductivity in an iron-based superconductor. }, keywords = {}, pubstate = {published}, tppubtype = {article} } A current of electrons with aligned spins can be used to modify magnetic order and superconductivity in an iron-based superconductor. | |
D. Valentinis; S. Gariglio; A. Fête; J.-M. Triscone; C. Berthod; D. van der Marel Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface Journal Article Physical Review B, 96 , pp. 094518, 2017. @article{Valentinis2017, title = {Modulation of the superconducting critical temperature due to quantum confinement at the LaAlO3/SrTiO3 interface}, author = {D. Valentinis and S. Gariglio and A. Fête and J.-M. Triscone and C. Berthod and D. van der Marel}, editor = {APS}, url = {https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.094518}, doi = {10.1103/PhysRevB.96.094518}, year = {2017}, date = {2017-09-18}, journal = {Physical Review B}, volume = {96}, pages = {094518}, abstract = {Superconductivity develops in bulk doped SrTiO3 and at the LaAlO3/SrTiO3 interface with a dome-shaped density dependence of the critical temperature Tc, despite different dimensionalities and geometries. We propose that the Tc dome of LaAlO3/SrTiO3 is a shape resonance due to quantum confinement of superconducting bulk SrTiO3. We substantiate this interpretation by comparing the exact solutions of a three-dimensional and quasi-two-dimensional two-band BCS gap equation. This comparison highlights the role of heavy bands for Tc in both geometries. For bulk SrTiO3, we extract the density dependence of the pairing interaction from the fit to experimental data. We apply quantum confinement in a square potential well of finite depth and calculate Tc in the confined configuration. We compare the calculated Tc to transport experiments and provide an explanation as to why the optimal Tc’s are so close to each other in two-dimensional interfaces and the three-dimensional bulk material. }, keywords = {}, pubstate = {published}, tppubtype = {article} } Superconductivity develops in bulk doped SrTiO3 and at the LaAlO3/SrTiO3 interface with a dome-shaped density dependence of the critical temperature Tc, despite different dimensionalities and geometries. We propose that the Tc dome of LaAlO3/SrTiO3 is a shape resonance due to quantum confinement of superconducting bulk SrTiO3. We substantiate this interpretation by comparing the exact solutions of a three-dimensional and quasi-two-dimensional two-band BCS gap equation. This comparison highlights the role of heavy bands for Tc in both geometries. For bulk SrTiO3, we extract the density dependence of the pairing interaction from the fit to experimental data. We apply quantum confinement in a square potential well of finite depth and calculate Tc in the confined configuration. We compare the calculated Tc to transport experiments and provide an explanation as to why the optimal Tc’s are so close to each other in two-dimensional interfaces and the three-dimensional bulk material. | |
Borroni, S.; Baldini, E.; Katukuri, V. M.; Mann, A.; Parlinski, K.; Legut, D.; Arrell, C.; van Mourik, F.; Teyssier, J.; Kozlowski, A.; Piekarz, P.; Yazyev, O. V.; Oleifmmode, A. M.; Lorenzana, J.; Carbone, F. Coherent generation of symmetry-forbidden phonons by light-induced electron-phonon interactions in magnetite Journal Article Phys. Rev. B, 96 , pp. 104308, 2017. @article{PhysRevB.96.104308, title = {Coherent generation of symmetry-forbidden phonons by light-induced electron-phonon interactions in magnetite}, author = {Borroni, S. and Baldini, E. and Katukuri, V. M. and Mann, A. and Parlinski, K. and Legut, D. and Arrell, C. and van Mourik, F. and Teyssier, J. and Kozlowski, A. and Piekarz, P. and Yazyev, O. V. and Oleifmmode, A. M. and Lorenzana, J. and Carbone, F.}, url = {https://link.aps.org/doi/10.1103/PhysRevB.96.104308}, doi = {10.1103/PhysRevB.96.104308}, year = {2017}, date = {2017-09-01}, journal = {Phys. Rev. B}, volume = {96}, pages = {104308}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Baldini E.; Mann A.; Benfatto L.; Cappelluti E.; Acocella A.; Silkin V. M.; Eremeev S. V.; Kuzmenko A. B.; Borroni S.; Tan T.; Xi X. X.; Zerbetto F.; Merlin R.; Carbone F. Real-Time Observation of Phonon-Mediated σ-π Interband Scattering in MgB2 Journal Article Phys. Rev. Lett., 119 (9), pp. 097002, 2017. @article{E.2017, title = {Real-Time Observation of Phonon-Mediated σ-π Interband Scattering in MgB2}, author = {Baldini E. and Mann A. and Benfatto L. and Cappelluti E. and Acocella A. and Silkin V. M. and Eremeev S. V. and Kuzmenko A. B. and Borroni S. and Tan T. and Xi X. X. and Zerbetto F. and Merlin R. and Carbone F.}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.119.097002}, doi = {10.1103/PhysRevLett.119.097002}, year = {2017}, date = {2017-08-31}, journal = {Phys. Rev. Lett.}, volume = {119}, number = {9}, pages = {097002}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Ubrig Nicolas; Jo Sanghyun; Philippi Marc; Costanzo Davide; Berger Helmuth; Kuzmenko Alexey B; Morpurgo Alberto F Microscopic Origin of the Valley Hall Effect in Transition Metal Dichalcogenides Revealed by Wavelength-Dependent Mapping Journal Article Nano Letters, 17 (9), pp. 5719-5725, 2017, ISSN: 1530-6984. @article{Nicolas2017, title = {Microscopic Origin of the Valley Hall Effect in Transition Metal Dichalcogenides Revealed by Wavelength-Dependent Mapping}, author = {Ubrig Nicolas and Jo Sanghyun and Philippi Marc and Costanzo Davide and Berger Helmuth and Kuzmenko Alexey B and Morpurgo Alberto F}, url = {https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.7b02666}, doi = {10.1021/acs.nanolett.7b02666}, issn = {1530-6984}, year = {2017}, date = {2017-08-27}, journal = {Nano Letters}, volume = {17}, number = {9}, pages = {5719-5725}, abstract = {The band structure of many semiconducting monolayer transition metal dichalcogenides (TMDs) possesses two degenerate valleys with equal and opposite Berry curvature. It has been predicted that, when illuminated with circularly polarized light, interband transitions generate an unbalanced nonequilibrium population of electrons and holes in these valleys, resulting in a finite Hall voltage at zero magnetic field when a current flows through the system. This is the so-called valley Hall effect that has recently been observed experimentally. Here, we show that this effect is mediated by photogenerated neutral excitons and charged trions and not by interband transitions generating independent electrons and holes. We further demonstrate an experimental strategy, based on wavelength dependent spatial mapping of the Hall voltage, which allows the exciton and trion contributions to the valley Hall effect to be discriminated in the measurement. These results represent a significant step forward in our understanding of the microscopic origin of photoinduced valley Hall effect in semiconducting transition metal dichalcogenides and demonstrate experimentally that composite quasi-particles, such as trions, can also possess a finite Berry curvature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The band structure of many semiconducting monolayer transition metal dichalcogenides (TMDs) possesses two degenerate valleys with equal and opposite Berry curvature. It has been predicted that, when illuminated with circularly polarized light, interband transitions generate an unbalanced nonequilibrium population of electrons and holes in these valleys, resulting in a finite Hall voltage at zero magnetic field when a current flows through the system. This is the so-called valley Hall effect that has recently been observed experimentally. Here, we show that this effect is mediated by photogenerated neutral excitons and charged trions and not by interband transitions generating independent electrons and holes. We further demonstrate an experimental strategy, based on wavelength dependent spatial mapping of the Hall voltage, which allows the exciton and trion contributions to the valley Hall effect to be discriminated in the measurement. These results represent a significant step forward in our understanding of the microscopic origin of photoinduced valley Hall effect in semiconducting transition metal dichalcogenides and demonstrate experimentally that composite quasi-particles, such as trions, can also possess a finite Berry curvature. | |
A. Tamai; Q. S. Wu; I. Cucchi; F. Y. Bruno; S. Riccò; T. K. Kim; M. Hoesch; C. Barreteau; E. Giannini; C. Besnard; A. A. Soluyanov; F. Baumberger Fermi Arcs and Their Topological Character in the Candidate Type-II Weyl Semimetal MoTe2 Journal Article Physical Review X, 6 (3), pp. 031021, 2017. @article{Tamai2017, title = {Fermi Arcs and Their Topological Character in the Candidate Type-II Weyl Semimetal MoTe2}, author = {A. Tamai and Q. S. Wu and I. Cucchi and F. Y. Bruno and S. Riccò and T. K. Kim and M. Hoesch and C. Barreteau and E. Giannini and C. Besnard and A. A. Soluyanov and F. Baumberger}, doi = {10.1103/PhysRevX.6.031021}, year = {2017}, date = {2017-08-17}, journal = {Physical Review X}, volume = {6}, number = {3}, pages = {031021}, abstract = {We report a combined experimental and theoretical study of the candidate type-II Weyl semimetal MoTe2. Using laser-based angle-resolved photoemission, we resolve multiple distinct Fermi arcs on the inequivalent top and bottom (001) surfaces. All surface states observed experimentally are reproduced by an electronic structure calculation for the experimental crystal structure that predicts a topological Weyl semimetal state with eight type-II Weyl points. We further use systematic electronic structure calculations simulating different Weyl point arrangements to discuss the robustness of the identified Weyl semimetal state and the topological character of Fermi arcs in MoTe2.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We report a combined experimental and theoretical study of the candidate type-II Weyl semimetal MoTe2. Using laser-based angle-resolved photoemission, we resolve multiple distinct Fermi arcs on the inequivalent top and bottom (001) surfaces. All surface states observed experimentally are reproduced by an electronic structure calculation for the experimental crystal structure that predicts a topological Weyl semimetal state with eight type-II Weyl points. We further use systematic electronic structure calculations simulating different Weyl point arrangements to discuss the robustness of the identified Weyl semimetal state and the topological character of Fermi arcs in MoTe2. | |
Ruppen, J.; Teyssier, J.; Ardizzone, I.; Peil, O. E.; Catalano, S.; Gibert, M.; Triscone, J.-M.; Georges, A.; van der Marel, D. Impact of antiferromagnetism on the optical properties of rare-earth nickelates Journal Article Phys. Rev. B, 96 , pp. 045120, 2017. @article{PhysRevB.96.045120, title = {Impact of antiferromagnetism on the optical properties of rare-earth nickelates}, author = {Ruppen, J. and Teyssier, J. and Ardizzone, I. and Peil, O. E. and Catalano, S. and Gibert, M. and Triscone, J.-M. and Georges, A. and van der Marel, D.}, url = {https://link.aps.org/doi/10.1103/PhysRevB.96.045120}, doi = {10.1103/PhysRevB.96.045120}, year = {2017}, date = {2017-07-01}, journal = {Phys. Rev. B}, volume = {96}, pages = {045120}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
D. Matera; M. Bonura; E. Giannini; C. Senatore Electrical Connectivity in MgB2: The Role of Precursors and Processing Routes in Controlling Voids and Detrimental Secondary Phases C Journal Article IEEE Transactions on Applied Superconductivity, 27 (4), pp. 1-6, 2017. @article{Matera2017, title = {Electrical Connectivity in MgB2: The Role of Precursors and Processing Routes in Controlling Voids and Detrimental Secondary Phases C}, author = {D. Matera and M. Bonura and E. Giannini and C. Senatore}, doi = {10.1109/TASC.2017.2654545}, year = {2017}, date = {2017-06-01}, journal = {IEEE Transactions on Applied Superconductivity}, volume = {27}, number = {4}, pages = {1-6}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
Manisha Chhikara; Iaroslav Gaponenko; Patrycja Paruch; Alexey B Kuzmenko Effect of uniaxial strain on the optical Drude scattering in graphene Journal Article 2D Materials, 4 (2), pp. 025081, 2017. @article{Chhikara2017, title = {Effect of uniaxial strain on the optical Drude scattering in graphene}, author = {Manisha Chhikara and Iaroslav Gaponenko and Patrycja Paruch and Alexey B Kuzmenko}, url = {https://doi.org/10.1088%2F2053-1583%2Faa6c10}, doi = {10.1088/2053-1583/aa6c10}, year = {2017}, date = {2017-04-28}, journal = {2D Materials}, volume = {4}, number = {2}, pages = {025081}, abstract = {Graphene is a mechanically robust 2D material promising for flexible optoelectronic applications. However, its electromagnetic properties under strain are experimentally poorly understood. Here we present the far-infrared transmission spectra of large-area chemical-vapor deposited monolayer graphene on a polyethylene terephthalate substrate subjected to uniaxial strain. The effective strain value is calibrated using the Raman spectroscopy and corrected for a relaxation of wrinkles and folds seen directly by atomic-force microscopy. We find that while the Drude weight and the Fermi level remain constant, the scattering rate increases by more than 10% per 1% of applied strain, showing a high level of reproducibility during strain cycling. As a result, the electronic mobility and optical absorption of graphene at terahertz and lower frequencies appear to also be sensitive to strain, which opens pathways to control these key parameters mechanically. We suggest that such a functionality can be potentially used in flexible optoelectronic and microelectromechanical systems based on graphene. By combining our findings with existing theoretical models, we discuss the possible mechanisms of strain-controlled Drude scattering.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene is a mechanically robust 2D material promising for flexible optoelectronic applications. However, its electromagnetic properties under strain are experimentally poorly understood. Here we present the far-infrared transmission spectra of large-area chemical-vapor deposited monolayer graphene on a polyethylene terephthalate substrate subjected to uniaxial strain. The effective strain value is calibrated using the Raman spectroscopy and corrected for a relaxation of wrinkles and folds seen directly by atomic-force microscopy. We find that while the Drude weight and the Fermi level remain constant, the scattering rate increases by more than 10% per 1% of applied strain, showing a high level of reproducibility during strain cycling. As a result, the electronic mobility and optical absorption of graphene at terahertz and lower frequencies appear to also be sensitive to strain, which opens pathways to control these key parameters mechanically. We suggest that such a functionality can be potentially used in flexible optoelectronic and microelectromechanical systems based on graphene. By combining our findings with existing theoretical models, we discuss the possible mechanisms of strain-controlled Drude scattering. | |
B. Hildebrand; T. Jaoue; C. Didiot; E. Razzoli; G. Monney; M.-L. Mottas, F. Vanini; C. Barreteau; A. Ubaldini; E. Giannini; H. Berger; D. R. Bowler; P. Aebi Local resilience of the 1T-TiSe2 charge density wave to Ti self-doping Journal Article Physical Review B, 95 (8), pp. 081104, 2017. @article{Hildebrand2017, title = {Local resilience of the 1T-TiSe2 charge density wave to Ti self-doping}, author = {B. Hildebrand and T. Jaoue and C. Didiot and E. Razzoli and G. Monney and M.-L. Mottas, F. Vanini and C. Barreteau and A. Ubaldini and E. Giannini and H. Berger and D. R. Bowler and P. Aebi}, doi = {10.1103/PhysRevB.95.081104}, year = {2017}, date = {2017-02-02}, journal = {Physical Review B}, volume = {95}, number = {8}, pages = {081104}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
J.-M. Poumirol; P. Q. Liu; T. M. Slipchenko; A. Y. Nikitin; L. Martin-Moreno; J. Faist; A. B. Kuzmenko Electrically controlled terahertz magneto-optical phenomena in continuous and patterned graphene Journal Article Nature Communications, 8 (14626), 2017. @article{Poumirol2017, title = {Electrically controlled terahertz magneto-optical phenomena in continuous and patterned graphene}, author = {J.-M. Poumirol and P. Q. Liu and T. M. Slipchenko and A. Y. Nikitin and L. Martin-Moreno and J. Faist and A. B. Kuzmenko}, editor = {Nature}, url = {http://www.nature.com/articles/ncomms14626}, doi = {10.1038/ncomms14626}, year = {2017}, date = {2017-01-18}, journal = {Nature Communications}, volume = {8}, number = {14626}, abstract = {The magnetic circular dichroism and the Faraday rotation are the fundamental phenomena of great practical importance arising from the breaking of the time reversal symmetry by a magnetic field. In most materials, the strength and the sign of these effects can be only controlled by the field value and its orientation. Furthermore, the terahertz range is lacking materials having the ability to affect the polarization state of the light in a non-reciprocal manner. Here we demonstrate, using broadband terahertz magneto-electro-optical spectroscopy, that in graphene both the magnetic circular dichroism and the Faraday rotation can be modulated in intensity, tuned in frequency and, importantly, inverted using only electrostatic doping at a fixed magnetic field. In addition, we observe strong magneto-plasmonic resonances in a patterned array of graphene antidots, which potentially allows exploiting these magneto-optical phenomena in a broad THz range.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The magnetic circular dichroism and the Faraday rotation are the fundamental phenomena of great practical importance arising from the breaking of the time reversal symmetry by a magnetic field. In most materials, the strength and the sign of these effects can be only controlled by the field value and its orientation. Furthermore, the terahertz range is lacking materials having the ability to affect the polarization state of the light in a non-reciprocal manner. Here we demonstrate, using broadband terahertz magneto-electro-optical spectroscopy, that in graphene both the magnetic circular dichroism and the Faraday rotation can be modulated in intensity, tuned in frequency and, importantly, inverted using only electrostatic doping at a fixed magnetic field. In addition, we observe strong magneto-plasmonic resonances in a patterned array of graphene antidots, which potentially allows exploiting these magneto-optical phenomena in a broad THz range. | |
I. Crassee; F. Borondics; M. K. Tran; G. Autès; A. Magrez; P. Bugnon; H. Berger; J. Teyssier; O. V. Yazyev; M. Orlita; A. Akrap BiTeCl and BiTeBr: A comparative high-pressure optical study Journal Article Physical Review B, 95 , pp. 045201, 2017. @article{Crassee2017, title = {BiTeCl and BiTeBr: A comparative high-pressure optical study}, author = {I. Crassee and F. Borondics and M. K. Tran and G. Autès and A. Magrez and P. Bugnon and H. Berger and J. Teyssier and O. V. Yazyev and M. Orlita and A. Akrap}, editor = {APS}, url = {http://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.045201}, doi = {10.1103/PhysRevB.95.045201}, year = {2017}, date = {2017-01-10}, journal = {Physical Review B}, volume = {95}, pages = {045201}, abstract = {We here report a detailed high-pressure infrared transmission study of BiTeCl and BiTeBr. We follow the evolution of two band transitions: the optical excitation β between two Rashba-split conduction bands, and the absorption γ across the band gap. In the low-pressure range, p<4 GPa, for both compounds β is approximately constant with pressure and γ decreases, in agreement with band structure calculations. In BiTeCl, a clear pressure-induced phase transition at 6 GPa leads to a different ground state. For BiTeBr, the pressure evolution is more subtle, and we discuss the possibility of closing and reopening of the band gap. Our data is consistent with a potential Weyl phase in BiTeBr at 5–6 GPa, followed by the onset of a structural phase transition above 7 GPa.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We here report a detailed high-pressure infrared transmission study of BiTeCl and BiTeBr. We follow the evolution of two band transitions: the optical excitation β between two Rashba-split conduction bands, and the absorption γ across the band gap. In the low-pressure range, p<4 GPa, for both compounds β is approximately constant with pressure and γ decreases, in agreement with band structure calculations. In BiTeCl, a clear pressure-induced phase transition at 6 GPa leads to a different ground state. For BiTeBr, the pressure evolution is more subtle, and we discuss the possibility of closing and reopening of the band gap. Our data is consistent with a potential Weyl phase in BiTeBr at 5–6 GPa, followed by the onset of a structural phase transition above 7 GPa. |