Thermal conductivity in the vicinity of the quantum critical endpoint in Sr3Ru2O7

TL;DR

This study measures thermal conductivity in Sr3Ru2O7 near its quantum critical endpoint, finding that the Wiedemann-Franz law holds at very low temperatures, indicating electron integrity despite non-Fermi liquid behavior.

Contribution

It provides experimental evidence that the Wiedemann-Franz law remains valid at the quantum critical point in Sr3Ru2O7, challenging theories predicting electron breakdown.

Findings

Wiedemann-Franz law satisfied within 5% at T -> 0 K across all fields

Disorder variation does not affect the validity of the law

Finite temperature behavior suggests ferromagnetic fluctuations influence non-Fermi liquid properties

Abstract

Thermal conductivity of Sr3Ru2O7 was measured down to 40 mK and at magnetic fields through the quantum critical endpoint at H_c = 7.85 T. A peak in the electrical resistivity as a function of field was mimicked by the thermal resistivity. In the limit as T -> 0 K we find that the Wiedemann-Franz law is satisfied to within 5% at all fields, implying that there is no breakdown of the electron despite the destruction of the Fermi liquid state at quantum criticality. A significant change in disorder (from $\rho_0$(H=0T) = 2.1 $\mu\Omega$ cm to 0.5 $\mu\Omega$ cm) does not influence our conclusions. At finite temperatures, the temperature dependence of the Lorenz number is consistent with ferromagnetic fluctuations causing the non-Fermi liquid behavior as one would expect at a metamagnetic quantum critical endpoint.