Browsing by Author "Wenzel, Maxim"

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    Low-temperature dielectric anomaly arising from electronic phase separation at the Mott insulator-metal transition
    (2021) Pustogow, Andrej; Rösslhuber, Roland; Tan, Yuting; Uykur, Ece; Böhme, Anette; Wenzel, Maxim; Saito, Yohei; Löhle, Anja; Hübner, Ralph; Kawamoto, Atsushi; Schlueter, John A.; Dobrosavljević, Vladimir; Dressel, Martin
    Coulomb repulsion among conduction electrons in solids hinders their motion and leads to a rise in resistivity. A regime of electronic phase separation is expected at the first-order phase transition between a correlated metal and a paramagnetic Mott insulator, but remains unexplored experimentally as well as theoretically nearby T = 0. We approach this issue by assessing the complex permittivity via dielectric spectroscopy, which provides vivid mapping of the Mott transition and deep insight into its microscopic nature. Our experiments utilizing both physical pressure and chemical substitution consistently reveal a strong enhancement of the quasi-static dielectric constant ε1 when correlations are tuned through the critical value. All experimental trends are captured by dynamical mean-field theory of the single-band Hubbard model supplemented by percolation theory. Our findings suggest a similar ’dielectric catastrophe’ in many other correlated materials and explain previous observations that were assigned to multiferroicity or ferroelectricity.
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    Pressure evolution of electron dynamics in the superconducting kagome metal CsV3Sb5
    (2023) Wenzel, Maxim; Tsirlin, Alexander A.; Capitani, Francesco; Chan, Yuk T.; Ortiz, Brenden R.; Wilson, Stephen D.; Dressel, Martin; Uykur, Ece
    The coexistence of the charge-density wave (CDW) and superconducting phases and their tunability under external pressure remains one of the key points in understanding the electronic structure of AV3Sb5 (A = K, Rb, Cs) kagome metals. Here, we employ synchrotron-based infrared spectroscopy assisted by density-functional calculations to study the pressure evolution of the electronic structure at room temperature up to 17 GPa experimentally. The optical spectrum of CsV3Sb5 is characterized by the presence of localized carriers seen as a broad peak at finite frequencies in addition to the conventional metallic Drude response. The non-monotonic pressure dependence of this low-energy peak reflects the re-entrant behavior of superconductivity and may be interpreted in terms of electron-phonon coupling, varying with the growth and shrinkage of the Fermi surface under pressure. Moreover, drastic modifications in the low-energy interband absorptions are observed upon the suppression of CDW. These changes are related to the upward shift of the Sb2 px + py band that eliminates part of the Fermi surface around the M-point, whereas band saddle points do not move significantly. These observations shed new light on the mixed electronic and lattice origin of the CDW in CsV3Sb5.