Abstract
Landau 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.
Highlights
Landau 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⋆
The correlation strength U/W is progressively reduced with x, allowing us to tune the system through the “bandwidth-controlled” Mott metalinsulator transition (MIT), covering a wide range in kBT/W and ħω/W within the parameter ranges accessible in our transport and optical experiments
Ρ(T) of κ-STFx (Fig. 2d) reveals a textbook Mott MIT resembling the pressure evolution of κ-(BEDT-TTF)[2] Cu2(CN)[317–19], which turns metallic around 1.3 kbar
Summary
Landau 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⋆. Since it is not possible to exhaustively model the interactions with all constituents of the crystal (nuclei and other electrons), Landau postulated quasiparticles (QP) with charge e and spin 12, which can be nearly free electrons but carry a renormalized mass treated as m⋆ that incorporates all interaction effects[1]. In his Fermi-liquid picture, the conductivity of metals scales with the QP lifetime τ, which increases asymptotically at low energy as the scattering phase space shrinks to zero[1]. The scattering rate is expected to saturate when the mean free path approaches the lattice spacing, known as Ioffe–Regel–Mott (IRM) limit[6,7]
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