Thermal conductivity through the quantum critical point in YbRh2Si2 at very low temperature

TL;DR

This study measures thermal conductivity in YbRh2Si2 at ultra-low temperatures, revealing an additional heat transport channel near the quantum critical point, challenging the magnon-based explanation and informing the Wiedemann-Franz law's validity.

Contribution

It provides new experimental evidence of heat transport behavior across the quantum critical point in YbRh2Si2 at very low temperatures.

Findings

Additional heat transport channel appears below 30 mK.

Magnons are excluded as the origin of the additional contribution.

Results impact the understanding of the Wiedemann-Franz law at quantum criticality.

Abstract

The thermal conductivity of YbRh2Si2 has been measured down to very low temperatures under field in the basal plane. An additional channel for heat transport appears below 30 mK, both in the antiferromagnetic and paramagnetic states, respectively below and above the critical field suppressing the magnetic order. This excludes antiferromagnetic magnons as the origin of this additional contribution to thermal conductivity. Moreover, this low temperature contribution prevails a definite conclusion on the validity or violation of the Wiedemann-Franz law at the field-induced quantum critical point. At high temperature in the paramagnetic state, the thermal conductivity is sensitive to ferromagnetic fluctuations, previously observed by NMR or neutron scattering and required for the occurrence of the sharp electronic spin resonance fracture.