Topic : Flawed Drude Behavior

Speaker : Prof. Martin Dressel, Universität Stuttgart, Germany

Date & Time : 2024. 07. 09 (Tue.) 11:00 AM

Place : Creative Learning Room 7F, SKKU Samsung Library

Abstract : 

When strong electronic interactions invalidate the assumptions of the Drude model, Landau suggested the ingenious solution, which modified the details while leaving the overall behavior intact. The low-energy properties of correlated 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* and scattering rate 1/*. The great success and wide applicability of Landau’s ideas cannot hide the fact that the celebrated quasiparticle concept breaks down when approaching and crossing the Mott transition or when the metal turns bad at elevated temperatures. Here we investigate the spectral and temperature-dependent complex electrodynamic response σ1(ω,T) + iσ2(ω,T) of molecular quantum materials as the influence of electronic interactions is varied [1]. 

We have chosen the quantum-spin-liquid candidate -(BEDT-TTF)2Cu2(CN)3 [2] as suitable model system because its effective correlation strength U/W can be easily varied by pressure or partial chemical substitution. For strongly-correlated Mott insulators the excitation spectrum is completely gapped, additional absorption occurs when entering the coexistence regime that appears at the first-order Mott transition below the critical endpoint [3]. Electronic phases of correlated metal and insulator are spatially separated: filling fraction and interaction strength vary concomitantly. 

Beyond the percolation threshold, on the metallic side, we reveal persistent Fermi-liquid behavior with T2 and ω2 dependences of the optical scattering rate γ(ω,T), along with a puzzling elastic contribution to relaxation. The strong increase of the resistivity beyond the Ioffe-Regel-Mott limit ρ ≫ ρIRM is accompanied by a displaced Drude peak in σ1(ω). 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 [4].

[1] M. Dressel and S. Tomić, Adv. Phys. 69, 1 (2020).

[2] B. Miksch et al., Science 372, 276 (2021)

[3] A. Pustogow et al., Nat. Mater. 17, 773 (2018); npj Quantum Mater. 6, 9 (2021).

[4] A. Pustogow et al., Nat. Commun. 12, 1571 (2021).