Nonvanishing Energy Scales at the Quantum Critical Point of CeCoIn5

TL;DR

This study investigates the quantum critical point in CeCoIn5 using heat and charge transport, revealing finite energy scales and persistent quasiparticles despite non-Fermi-liquid behavior at the critical field.

Contribution

It provides evidence that quasiparticles survive at the quantum critical point with finite energy scales, challenging traditional Fermi-liquid expectations.

Findings

Fermi-liquid regime vanishes at critical field

Finite spin fluctuation temperature at criticality

Quasiparticles remain intact at the quantum critical point

Abstract

Heat and charge transport were used to probe the magnetic field-tuned quantum critical point in the heavy-fermion metal CeCoIn$_5$. A comparison of electrical and thermal resistivities reveals three characteristic energy scales. A Fermi-liquid regime is observed below $T_{FL}$, with both transport coefficients diverging in parallel and $T_{FL}\to 0$ as $H\to H_c$, the critical field. The characteristic temperature of antiferromagnetic spin fluctuations, $T_{SF}$, is tuned to a minimum but {\it finite} value at $H_c$, which coincides with the end of the $T$-linear regime in the electrical resistivity. A third temperature scale, $T_{QP}$, signals the formation of quasiparticles, as fermions of charge $e$ obeying the Wiedemann-Franz law. Unlike $T_{FL}$, it remains finite at $H_c$, so that the integrity of quasiparticles is preserved, even though the standard signature of Fermi-liquid theory fails.