08 Fakultät Mathematik und Physik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/9
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Item Open Access Tuning charge order in (TMTTF)2X by partial anion substitution(2021) Pustogow, Andrej; Dizdarevic, Daniel; Erfort, Sebastian; Iakutkina, Olga; Merkl, Valentino; Untereiner, Gabriele; Dressel, MartinIn the quasi-one-dimensional (TMTTF)2X compounds with effectively quarter-filled bands, electronic charge order is stabilized from the delicate interplay of Coulomb repulsion and electronic bandwidth. The correlation strength is commonly tuned by physical pressure or chemical substitution with stoichiometric ratios of anions and cations. Here, we investigate the charge-ordered state through partial substitution of the anions in (TMTTF)2[AsF6]1-x[SbF6]x with x≈0.3, determined from the intensity of infrared vibrations, which is sufficient to suppress the spin-Peierls state. Our dc transport experiments reveal a transition temperature TCO = 120 K and charge gap ΔCO=430 K between the values of the two parent compounds (TMTTF)2AsF6 and (TMTTF)2SbF6. Upon plotting the two parameters for different (TMTTF)2X, we find a universal relationship between TCO and ΔCO yielding that the energy gap vanishes for transition temperatures TCO≤60 K. While these quantities indicate that the macroscopic correlation strength is continuously tuned, our vibrational spectroscopy results probing the local charge disproportionation suggest that 2δ is modulated on a microscopic level.Item Open Access Rise and fall of Landau’s quasiparticles while approaching the Mott transition(2021) Pustogow, Andrej; Saito, Yohei; Löhle, Anja; Sanz Alonso, Miriam; Kawamoto, Atsushi; Dobrosavljević, Vladimir; Dressel, Martin; Fratini, SimoneLandau suggested that the low-temperature properties of metals can be understood in terms of long-lived quasiparticles with all complex interactions included in Fermi-liquid parameters, such as the effective mass m⋆. Despite its wide applicability, electronic transport in bad or strange metals and unconventional superconductors is controversially discussed towards a possible collapse of the quasiparticle concept. Here we explore the electrodynamic response of correlated metals at half filling for varying correlation strength upon approaching a Mott insulator. We reveal persistent Fermi-liquid behavior with pronounced quadratic dependences of the optical scattering rate on temperature and frequency, along with a puzzling elastic contribution to relaxation. The strong increase of the resistivity beyond the Ioffe-Regel-Mott limit is accompanied by a ‘displaced Drude peak’ in the optical conductivity. Our results, supported by a theoretical model for the optical response, demonstrate the emergence of a bad metal from resilient quasiparticles that are subject to dynamical localization and dissolve near the Mott transition.Item Open Access Fractional power-law intraband optical conductivity in the low-dimensional Dirac material CaMnBi2(2021) Schilling, Micha Benjamin; Wang, C. X.; Shi, You-Guo; Kremer, Reinhard Karl; Dressel, Martin; Pronin, Artem V.We studied the broadband optical conductivity of CaMnBi2, a material with two-dimensional Dirac electronic bands, and found that both components of the intraband conductivity follow a universal power law as a function of frequency at low temperatures. This conductivity scaling differs from the Drude(-like) behavior, generally expected for free carriers, but matches the predictions for the intraband response of an electronic system in a quantum critical region. Since no other indications of quantum criticality are reported for CaMnBi2 so far, the cause of the observed unusual scaling remains an open question.Item Open Access 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, MartinCoulomb 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.Item Open Access Dielectric anomaly and charge fluctuations in the non-magnetic dimer Mott insulator λ-(BEDT-STF)2GaCl4(2021) Iakutkina, Olga; Rösslhuber, Roland; Kawamoto, Atsushi; Dressel, MartinThe dimer Mott insulator l-(BEDT-STF)2GaCl4 undergoes no magnetic order down to the lowest temperatures, suggesting the formation of a novel quantum disordered state. Our frequency and temperature-dependent investigations of the dielectric response reveal a relaxor-like behavior below T ≈ 100 K for all three axes, similar to other spin liquid candidates. Optical measurement of the charge-sensitive vibrational mode n27(b1u) identifies a charge disproportionation Dr ≈ 0.04e on the dimer that exists up to room temperature and originates from inequivalent molecules in the weakly coupled dimers. The linewidth of the charge sensitive mode is broader than that of typical organic conductors, supporting the existence of a disordered electronic state.Item 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, MartinMultivalley 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.Item Open Access Pressure-tuned superconducting dome in chemically-substituted κ-(BEDT-TTF)2Cu2(CN)3(2021) Saito, Yohei; Löhle, Anja; Kawamoto, Atsushi; Pustogow, Andrej; Dressel, MartinThe quantum spin liquid candidate 𝜅-(BEDT-TTF)2Cu2(CN)3 has been established as the prime example of a genuine Mott insulator that can be tuned across the first-order insulator–metal transition either by chemical substitution or by physical pressure. Here, we explore the superconducting state that occurs at low temperatures, when both methods are combined, i.e., when 𝜅-[(BEDT-TTF)1-𝑥(BEDT-STF)𝑥]2Cu2(CN)3 is pressurized. We discovered superconductivity for partial BEDT-STF substitution with x = 0.10–0.12 even at ambient pressure, i.e., a superconducting state is realized in the range between a metal and a Mott insulator without magnetic order. Furthermore, we observed the formation of a superconducting dome by pressurizing the substituted crystals; we assigned this novel behavior to disorder emanating from chemical tuning.Item Open Access Characterization of harmonic modes and parasitic resonances in multi-mode superconducting coplanar resonators(2023) Beydeda, Cenk; Nikolaou, Konstantin; Tochtermann, Marius; Ebensperger, Nikolaj G.; Untereiner, Gabriele; Farag, Ahmed; Karl, Philipp; Ubl, Monika; Giessen, Harald; Dressel, Martin; Scheffler, MarcItem 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.Item 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, EceThe 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.