Two Routes from Mott Insulators to Metals: Dynamics of Correlated Charge Carriers

• Applicant: Professor Dr. Martin Dressel
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2012 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 200045292

• Final Report Year: 2024

Final Report Abstract

Two Routes from Mott Insulators to Metals: Dynamics of Correlated Charge Carriers At the Mott transition, metals are driven to an insulating state when the electron-electron repulsion increases strongly. As with any first-order phase transition (e.g. water and ice), there is a regime of coexistence in the phase diagram where metallic and insulating regions coexist, with the ratio of the two components varying with temperature and correlation strength. This electronic phase separation leads to a divergence of the dielectric constant near the percolation threshold, as our pressure- and temperature-dependent optical and dielectric measurements on organic conductors show for the first time. By combining quantum mechanical DMFT calculations with the effective medium theory, the behavior is also modeled theoretically. It was of great advantage of using quantum spin liquids as model systems that no magnetic order occurs down to lowest temperatures, and thus the purely electronic phase diagram can be investigated. We suspect that a region of coexistence and inhomogeneity also occurs in other metal-insulator phase transitions and suggest investigations in this regard. With dielectric spectroscopy, we were also able to establish a macroscopic method that provides insights into the microscopic structure of the bulk materials and can also be used under extreme conditions (high but also ultra-low temperatures, high pressures or strong magnetic fields). Moreover, despite their essentially metallic behavior, the electrodynamic properties of strongly correlated electron systems show a maximum in the optical conductivity at finite frequencies. This displaced Drude peak indicates an incipient localization of the metallic charge carriers as proposed by a theory of transient localization. Further investigations will shed light on the temperature behavior of the incipient localization and the scaling with the interaction strength. We were able to determine the temperature and frequency dependence of the electronic scattering rate: the quadratic temperature curve of the resistance commonly observed corresponds to a quadratic increase with frequency. For the first time, we were able to quantitatively determine ω/T scaling in the Fermi-liquid range as a function of the correlation strength. These observations will be extended to transition metal oxides, which, however, have a significantly higher energy scale (temperature and frequency).

Publications

• Transition of a pristine Mott insulator to a correlated Fermi liquid: Pressure-dependent optical investigations of a quantum spin liquid. Physical Review B, 99(11).
  Li, Weiwu; Pustogow, Andrej; Kato, Reizo & Dressel, Martin
  
• Molecular quantum materials: electronic phases and charge dynamics in two-dimensional organic solids. Advances in Physics, 69(1), 1-120.
  Dressel, Martin & Tomić, Silvia
  
• Charge localization in strongly correlated κ−(BEDT−TTF)2Cu[N(CN)2]I due to inherent disorder. Physical Review B, 104(20).
  Iakutkina, O.; Majer, L. N.; Biesner, T.; Uykur, E.; Schlueter, J. A. & Dressel, M.
  
• Chemical tuning of molecular quantum materials κ-[(BEDT-TTF)1−x(BEDT-STF)x]2Cu2(CN)3: from the Mott-insulating quantum spin liquid to metallic Fermi liquid. Journal of Materials Chemistry C, 9(33), 10841-10850.
  Saito, Yohei; Rösslhuber, Roland; Löhle, Anja; Sanz, Alonso Miriam; Wenzel, Maxim; Kawamoto, Atsushi; Pustogow, Andrej & Dressel, Martin
  
• Dielectric Anomaly and Charge Fluctuations in the Non-Magnetic Dimer Mott Insulator λ-(BEDT-STF)2GaCl4. Crystals, 11(9), 1031.
  Iakutkina, Olga; Rosslhuber, Roland; Kawamoto, Atsushi & Dressel, Martin
  
• Low-temperature dielectric anomaly arising from electronic phase separation at the Mott insulator-metal transition. npj Quantum Materials, 6(1).
  Pustogow, A.; Rösslhuber, R.; Tan, Y.; Uykur, E.; Böhme, A.; Wenzel, M.; Saito, Y.; Löhle, A.; Hübner, R.; Kawamoto, A.; Schlueter, J. A.; Dobrosavljević, V. & Dressel, M.
  
• Phase coexistence at the first-order Mott transition revealed by pressure-dependent dielectric spectroscopy of κ−(BEDT−TTF)2Cu2(CN)3. Physical Review B, 103(12).
  Rösslhuber, R.; Pustogow, A.; Uykur, E.; Böhme, A.; Löhle, A.; Hübner, R.; Schlueter, J. A.; Tan, Y.; Dobrosavljević, V. & Dressel, M.
  
• Pressure-Tuned Superconducting Dome in Chemically-Substituted κ-(BEDT-TTF)2Cu2(CN)3. Crystals, 11(7), 817.
  Saito, Yohei; Löhle, Anja; Kawamoto, Atsushi; Pustogow, Andrej & Dressel, Martin
  
• Rise and fall of Landau’s quasiparticles while approaching the Mott transition. Nature Communications, 12(1).
  Pustogow, Andrej; Saito, Yohei; Löhle, Anja; Sanz, Alonso Miriam; Kawamoto, Atsushi; Dobrosavljević, Vladimir; Dressel, Martin & Fratini, Simone
  
• Effect of hydrostatic pressure on the quantum paraelectric state of dipolar coupled water molecular network. Physical Review Research, 4(2).
  Chan, Y. T.; Uykur, E.; Belyanchikov, M. A.; Dressel, M.; Abalmasov, V. A.; Thomas, V.; Zhukova, E. S. & Gorshunov, B.
  
• High-pressure investigations in CH3NH3PbX3 (X = I, Br, and Cl): Suppression of ion migration and stabilization of low-temperature structure. Physical Review B, 106(21).
  Chan, Yuk Tai; Elliger, Natanja; Klis, Berina; Kollár, Márton; Horváth, Endre; Forró, László; Dressel, Martin & Uykur, Ece
  
• Pressure-dependent dielectric response of the frustrated Mott insulator κ-(BEDTTTF)2 Ag2(CN)3. Physical Review B, 107(7).
  Rösslhuber, R.; Hübner, R.; Dressel, M. & Pustogow, A.
  
• Radio frequency dielectric measurements in diamond anvil cells. Review of Scientific Instruments, 94(2).
  Chan, Yuk Tai; Uykur, Ece & Dressel, Martin