Reconciling strange metal transport in CeCoIn$_5$ through the difference of optical and cyclotron effective masses

TL;DR

This study investigates the optical and cyclotron effective masses in CeCoIn$_5$, revealing a hidden Fermi liquid behavior with a T$^2$ relaxation rate and a temperature-dependent optical mass, reconciling strange metal transport phenomena.

Contribution

The paper demonstrates that the optical mass in CeCoIn$_5$ scales as 1/T, contrasting with the cyclotron mass, and explains strange metal transport through this mass difference, revealing FL-like physics.

Findings

Current relaxation rate scales as T$^2$

Optical mass scales roughly as 1/T

Reconciliation of linear resistivity with Fermi liquid behavior

Abstract

The strange metal behavior in cuprate superconductors - characterized by linear in temperature resistivity and anomalous Hall transport - stands in stark contrast to the expectation of conventional Fermi liquid (FL) theory. Remarkably, the similar transport behavior has also been observed in the heavy fermion metal CeCoIn$_5$, whose d-wave superconducting ground state and strong antiferromagnetic fluctuations draw parallels to the cuprates. Here we have investigated the optical conductivity of the strange metal state of CeCoIn$_5$ over a wide magnetic field range using time-domain THz spectroscopy (TDTS). Using unique high-field THz spectroscopy we have shown that the current relaxation rate scales approximately as T$^2$, giving evidence for a hidden Fermi liquid state over a large field range. This result can be reconciled with linear in T resistivity with the realization that heavy quasiparticles have an optical mass that scales roughly like 1/T. This optical mass contrasts with the mass that characterizes cyclotron motion, which does not suffer the same large temperature dependent renormalization. Although by itself anomalous, this allows one to understand a number of other phenomena in CeCoIn$_5$ that have been taken to be signatures of strange metals, including the coexistence of a conventional T$^2$ dependence of the cotangent of the Hall angle with the linear in T resistivity, which with our observation also reflects FL-like physics.