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Your search keyword '"Gallais, Yann"' showing total 8 results
Start Over Author "Gallais, Yann" Topic strongly correlated electrons (cond-mat.str-el)
8 results on '"Gallais, Yann"'

1. Disentangling lattice and electronic instabilities in the excitonic insulator candidate Ta$_2$NiSe$_5$ by nonequilibrium spectroscopy

Author

Katsumi, Kota, Alekhin, Alexandr, Souliou, Sofia-Michaela, Merz, Michael, Haghighirad, Amir-Abbas, Tacon, Matthieu Le, Houver, Sarah, Cazayous, Maximilien, Sacuto, Alain, and Gallais, Yann

Subjects
Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), FOS: Physical sciences
Abstract

Ta$_2$NiSe$_5$ is an excitonic insulator candidate showing the semiconductor/semimetal-to-insulator (SI) transition below $T_{\text{c}}$ = 326 K. However, since a structural transition accompanies the SI transition, deciphering the role of electronic and lattice degrees of freedom in driving the SI transition has remained controversial. Here, we investigate the photoexcited nonequilibrium state in Ta$_2$NiSe$_5$ using pump-probe Raman and photoluminescence (PL) spectroscopies. The combined nonequilibrium spectroscopic measurements of the lattice and electronic states reveal the presence of a photoexcited metastable state where the insulating gap is suppressed, but the low-temperature structural distortion is preserved. We conclude that electron correlations play a vital role in the SI transition of Ta$_2$NiSe$_5$., 13 pages, 10 figures

Published
2022

2. Elasto-Raman scattering: arsenic optical phonon as a probe of nematicity in BaFe$_2$As$_2$

Author

Philippe, Jean-Côme, Faria, Jimmy, Forget, Anne, Colson, Dorothée, Houver, Sarah, Cazayous, Maximilien, Sacuto, Alain, Gallais, Yann, Laboratoire Matériaux et Phénomènes Quantiques (MPQ (UMR_7162)), Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Service de physique de l'état condensé (SPEC - UMR3680), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire Nano-Magnétisme et Oxydes (LNO), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Institut Rayonnement Matière de Saclay (IRAMIS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, and ANR-18-CE92-0020,IFAS,Interaction entre ferroélctricité et la supraconductivité(2018)

Subjects
Condensed Matter::Soft Condensed Matter, Superconductivity (cond-mat.supr-con), Condensed Matter - Strongly Correlated Electrons, Condensed Matter::Materials Science, Strongly Correlated Electrons (cond-mat.str-el), Condensed Matter - Superconductivity, FOS: Physical sciences, [PHYS.COND]Physics [physics]/Condensed Matter [cond-mat]
Abstract

We report a Raman scattering study of nematic degrees of freedom in the iron-based superconductor parent compound BaFe$_2$As$_2$ under tunable uniaxial strain. We demonstrate that the polarization resolved arsenic (As) phonon intensity can be used to monitor the nematic order parameter as a function of both temperature and strain. At low temperature in the nematic ordered phase we use it to track the continuous and reversible orientation of nematic domains under variable strain. At higher temperature, the evolution of the As phonon intensity under strain reflects an enhanced nematic susceptibility close to the nematic transition $T_S$. Its temperature dependence under strong strain follows qualitatively the expected behavior of an Ising order parameter under a symmetry breaking field. Our elasto-Raman study illustrates the interest of combining selective anisotropic strain with a symmetry resolved probe like Raman scattering. Elasto-Raman scattering can be applied to a wide variety of quantum materials where uniaxial strain tunes electronic orders., Comment: 14 pages (including appendix), 11 figures

Published
2021
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3. Magnon bound states vs. anyonic Majorana excitations in the Kitaev honeycomb magnet $��$-RuCl$_3$

Author

Wulferding, Dirk, Choi, Youngsu, Do, Seung-Hwan, Lee, Chan Hyeon, Lemmens, Peter, Faugeras, Clement, Gallais, Yann, and Choi, Kwang-Yong

Subjects
Strongly Correlated Electrons (cond-mat.str-el), FOS: Physical sciences
Abstract

The pure Kitaev honeycomb model harbors a quantum spin liquid in zero magnetic fields, while applying finite magnetic fields induces a topological spin liquid with non-Abelian anyonic excitations. This latter phase has been much sought after in Kitaev candidate materials, such as $��$-RuCl$_3$. Currently, two competing scenarios exist for the intermediate field phase of this compound ($B=7-10$ T), based on experimental as well as theoretical results: (i) conventional multiparticle magnetic excitations of integer quantum number vs. (ii) Majorana fermionic excitations of possibly non-Abelian nature with a fractional quantum number. To discriminate between these scenarios a detailed investigation of excitations over a wide field-temperature phase diagram is essential. Here we present Raman spectroscopic data revealing low-energy quasiparticles emerging out of a continuum of fractionalized excitations at intermediate fields, which are contrasted by conventional spin-wave excitations. The temperature evolution of these quasiparticles suggests the formation of bound states out of fractionalized excitations.

Published
2019
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4. Pressure induced collapse of the charge density wave and Higgs mode visibility in 2H-TaS$_2$

Author

Grasset, Romain, Gallais, Yann, Sacuto, Alain, Cazayous, Maximilien, Ma��as-Valero, Samuel, Coronado, Eugenio, and M��asson, Marie-Aude

Subjects
Superconductivity (cond-mat.supr-con), Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), Condensed Matter::Superconductivity, Condensed Matter - Superconductivity, FOS: Physical sciences
Abstract

The pressure evolution of the Raman active electronic excitations of the transition metal dichalcogenides 2H-TaS$_2$ is followed through the pressure phase diagram embedding incommensurate charge-density-wave and superconducting states. At high pressure, the charge-density-wave is found to collapse at 8.5~GPa. In the coexisting charge-density-wave and superconducting orders, we unravel a strong in-gap superconducting mode, attributed to a Higgs mode, coexisting with the expected incoherent Cooper-pair breaking signature. The latter remains in the pure superconducting state reached above 8.5~GPa. Our report constitutes the first observation of such Raman active Higgs mode since the longstanding unique case 2H-NbSe$_2$., 6 pages, 3 figures. Supplementary Material available upon request

Published
2018

5. Higgs mode in the d-wave superconductor Bi2Sr2CaCu2O8+x driven by an intense terahertz pulse

Author

Katsumi, Kota, Tsuji, Naoto, Hamada, Yuki I., Matsunaga, Ryusuke, Schneeloch, John, Zhong, Ruidan D., Gu, Genda. D., Aoki, Hideo, Gallais, Yann, and Shimano, Ryo

Subjects
Superconductivity (cond-mat.supr-con), Condensed Matter - Strongly Correlated Electrons, Strongly Correlated Electrons (cond-mat.str-el), Condensed Matter - Superconductivity, Condensed Matter::Superconductivity, Physics::Optics, FOS: Physical sciences
Abstract

We investigated the terahertz (THz)-pulse driven nonlinear response in the d-wave cuprate superconductor Bi2Sr2CaCu2O8+x (Bi2212) using a THz pump near-infrared probe scheme in the time domain. We have observed an oscillatory behavior of the optical reflectivity that follows the THz electric field squared and is strongly enhanced below Tc. The corresponding third-order nonlinear effect exhibits both A1g and B1g symmetry components, which are decomposed from polarization-resolved measurements. Comparison with a BCS calculation of the nonlinear susceptibility indicates that the A1g component is associated with the Higgs mode of the d-wave order parameter., Comment: 14 pages, 4 figures + supplemental material

Published
2017
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6. A ferroelectric quantum phase transition inside the superconducting dome of Sr$_{1-x}$Ca$_{x}$TiO$_{3-��}$

Author

Rischau, Carl Willem, Lin, Xiao, Grams, Christoph P., Finck, Dennis, Harms, Steffen, Engelmayer, Johannes, Lorenz, Thomas, Gallais, Yann, Fauqu��, Beno��t, Hemberger, Joachim, and Behnia, Kamran

Subjects
Superconductivity (cond-mat.supr-con), Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences
Abstract

SrTiO$_{3}$, a quantum paraelectric, becomes a metal with a superconducting instability after removal of an extremely small number of oxygen atoms. It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium. The two orders may be accidental neighbors or intimately connected, as in the picture of quantum critical ferroelectricity. Here, we show that in Sr$_{1-x}$Ca$_{x}$TiO$_{3-��}$ ($0.002, Accepted by Nature Physics. A slightly modified version will appear on the journal's website soon

Published
2017
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7. Lattice dynamics of the heavy-fermion compound URu2Si2

Author

Buhot, J., Measson, M. A., Gallais, Yann, Cazayous, M., Sacuto, A., Bourdarot, Frédéric, Raymond, stéphane, Lapertot, Gérard, Aoki, Dai, Regnault, Louis-Pierre, Ivanov, A., Piekarz, P., Parlinski, K., Legut, D., Homes, C. C., Lejay, P., Lobo, R. P. S. M., Laboratoire Matériaux et Phénomènes Quantiques (MPQ (UMR_7162)), Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Magnétisme et Diffusion Neutronique (MDN), Modélisation et Exploration des Matériaux (MEM), Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Instrumentation, Material and Correlated Electrons Physics (IMAPEC), PHotonique, ELectronique et Ingénierie QuantiqueS (PHELIQS), Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Tohoku University [Sendai], Institut Laue-Langevin (ILL), ILL, Inst. Nucl. Phys., Polska Akademia Nauk = Polish Academy of Sciences (PAN), Brookhaven National Laboratory [Upton, NY] (BNL), U.S. Department of Energy [Washington] (DOE)-UT-Battelle, LLC-Stony Brook University [SUNY] (SBU), State University of New York (SUNY)-State University of New York (SUNY), Cristaux Massifs (CrisMass), Institut Néel (NEEL), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et d'Etude des Matériaux (UMR 8213) (LPEM), Ecole Superieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), ANR-11-IDEX-0005,USPC,Université Sorbonne Paris Cité(2011), ANR-11-BS04-0002,PRINCESS,Instrumentation et études novatrices sur les systèmes à électrons corrélés sous pression(2011), UT-Battelle, LLC-Stony Brook University [SUNY] (SBU), State University of New York (SUNY)-State University of New York (SUNY)-U.S. Department of Energy [Washington] (DOE), Croissance Cristalline et MicroAnalyse (NEEL - C2MA), Université Grenoble Alpes (UGA)-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Grenoble Alpes (UGA)-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut de Recherche Interdisciplinaire de Grenoble (IRIG), Polska Akademia Nauk (PAN), Brookhaven National Laboratory [Upton] (BNL), Stony Brook University [SUNY] (SBU), CrisMass - Cristaux Massifs, Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF), Laboratoire de Physique et d'Etude des Matériaux (LPEM), Centre National de la Recherche Scientifique (CNRS)-ESPCI ParisTech-Université Pierre et Marie Curie - Paris 6 (UPMC), and ANR-11-IDEX-0005-02/10-LABX-0096,SEAM,Science and Engineering for Advanced Materials and devices(2011)

Subjects
Symmetry-Breaking, [PHYS]Physics [physics], Strongly Correlated Electrons (cond-mat.str-el), Transitions, FOS: Physical sciences, Hidden-Order, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, Magnetic Excitations, Condensed Matter - Strongly Correlated Electrons, Samples, Superconductor URu2Si2, Phase, Phonons, Condensed Matter::Strongly Correlated Electrons, System URu2Si2, Raman-Scattering
Abstract

We report a comprehensive investigation of the lattice dynamics of URu$_2$Si$_2$ as a function of temperature using Raman scattering, optical conductivity and inelastic neutron scattering measurements as well as theoretical {\it ab initio} calculations. The main effects on the optical phonon modes are related to Kondo physics. The B$_{1g}$ ($\Gamma_3$ symmetry) phonon mode slightly softens below $\sim$100~K, in connection with the previously reported softening of the elastic constant, $C_{11}-C_{12}$, of the same symmetry, both observations suggesting a B$_{1g}$ symmetry-breaking instability in the Kondo regime. Through optical conductivity, we detect clear signatures of strong electron-phonon coupling, with temperature dependent spectral weight and Fano line shape of some phonon modes. Surprisingly, the line shapes of two phonon modes, E$_u$(1) and A$_{2u}$(2), show opposite temperature dependencies. The A$_{2u}$(2) mode loses its Fano shape below 150 K, whereas the E$_u$(1) mode acquires it below 100~K, in the Kondo cross-over regime. This may point out to momentum-dependent Kondo physics. By inelastic neutron scattering measurements, we have drawn the full dispersion of the phonon modes between 300~K and 2~K. No remarkable temperature dependence has been obtained including through the hidden order transition. {\it Ab initio} calculations with the spin-orbit coupling are in good agreement with the data except for a few low energy branches with propagation in the (a,b) plane.

Published
2015
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8. Lattice and spin excitations in multiferroic h-YMnO3

Author

Toulouse, Constance, Liu, Jiaji, Gallais, Yann, Measson, Marie-Aude, Sacuto, Alain, Cazayous, Maximilien, Chaix, Laura, Simonet, Virginie, de Brion, Sophie, Pinsard-Godart, Loreynne, Willaert, Fabrice, Brubach, Jean-Blaise, Roy, Pascale, Petit, Sylvain, Laboratoire Matériaux et Phénomènes Quantiques (MPQ (UMR_7162)), Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Matériaux, Rayonnements, Structure (MRS), Institut Néel (NEEL), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS), Institut Laue-Langevin (ILL), ILL, Magnétisme et Supraconductivité (MagSup), Laboratoire de Chimie des Solides, Université Paris-Sud - Paris 11 (UP11)-Centre National de la Recherche Scientifique (CNRS), Ligne AILES, Synchrotron SOLEIL, Laboratoire Léon Brillouin (LLB - UMR 12), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay, MRS - Matériaux, Rayonnements, Structure, Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF), MagSup - Magnétisme et Supraconductivité, Matériaux, Rayonnements, Structure (NEEL - MRS), Magnétisme et Supraconductivité (NEEL - MagSup), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science, Condensed Matter::Materials Science, Strongly Correlated Electrons (cond-mat.str-el), Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences, Condensed Matter::Strongly Correlated Electrons, [PHYS.COND.CM-SCE]Physics [physics]/Condensed Matter [cond-mat]/Strongly Correlated Electrons [cond-mat.str-el], ComputingMilieux_MISCELLANEOUS
Abstract

We used Raman and terahertz spectroscopies to investigate lattice and magnetic excitations and their cross-coupling in the hexagonal YMnO3 multiferroic. Two phonon modes are strongly affected by the magnetic order. Magnon excitations have been identified thanks to comparison with neutron measurements and spin wave calculations but no electromagnon has been observed. In addition, we evidenced two additional Raman active peaks. We have compared this observation with the anti-crossing between magnon and acoustic phonon branches measured by neutron. These optical measurements underly the unusual strong spin-phonon coupling.

Published
2014
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