Browsing by Author "Tsirlin, Alexander A."

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Open Access
Optical detection of the density-wave instability in the kagome metal KV3Sb5
(2022) Uykur, Ece; Ortiz, Brenden R.; Wilson, Stephen D.; Dressel, Martin; Tsirlin, Alexander A.
Coexisting density-wave and superconducting states along with the large anomalous Hall effect in the absence of local magnetism remain intriguing and enigmatic features of the AV3Sb5 kagome metals (A = K, Rb, Cs). Here, we demonstrate via optical spectroscopy and density-functional calculations that low-energy dynamics of KV3Sb5 is characterized by unconventional localized carriers, which are strongly renormalized across the density-wave transition and indicative of electronic correlations. Strong phonon anomalies are prominent not only below the density-wave transition, but also at high temperatures, suggesting an intricate interplay of phonons with the underlying electronic structure. We further propose the star-of-David and tri-hexagon (inverse star-of-David) configurations for the density-wave order in KV3Sb5. These configurations are strongly reminiscent of p-wave states expected in the Hubbard model on the kagome lattice at the filling level of the van Hove singularity. The proximity to this regime should have intriguing and far-reaching implications for the physics of KV3Sb5 and related materials.
Open Access
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.
Open Access
Spectroscopic trace of the Lifshitz transition and multivalley activation in thermoelectric SnSe under high pressure
(2021) Biesner, Tobias; Li, Weiwu; Tsirlin, Alexander A.; Roh, Seulki; Wei, Pai-Chun; Uykur, Ece; Dressel, Martin
Multivalley systems offer not only exciting physical phenomena but also the possibility of broad utilization. Identifying an important platform and understanding its physics are paramount tasks to improve their capability for application. Here, we investigate a promising candidate, the semiconductor SnSe, by optical spectroscopy and density functional theory calculations. Upon applying pressure to lightly doped SnSe, we directly monitored the phase transition from semiconductor to semimetal. In addition, heavily doped SnSe exhibited a successive Lifshitz transition, activating multivalley physics. Our comprehensive study provides insight into the effects of pressure and doping on this system, leading to promising routes to tune the material properties for advanced device applications, including thermoelectrics and valleytronics.