Low-temperature thermopower study of YbRh2Si2

TL;DR

This study investigates the low-temperature thermopower of YbRh2Si2, revealing non-Fermi-liquid behavior near the quantum critical point and the recovery of Fermi-liquid behavior at higher magnetic fields.

Contribution

It provides detailed thermopower measurements down to 30 mK, showing sign changes and crossover behavior associated with quantum criticality in YbRh2Si2.

Findings

Sign change in thermopower at the QCP

Recovery of Fermi-liquid behavior at B > Bc

Crossover temperature matches resistivity and specific heat data

Abstract

The heavy-fermion compound YbRh2Si2 exhibits an antiferromagnetic (AFM) phase transition at an extremely low temperature of TN = 70 mK. Upon applying a tiny magnetic field of Bc = 60 mT the AFM ordering is suppressed and the system is driven toward a field-induced quantum critical point (QCP). Here, we present low-temperature thermopower S(T) measurements of high-quality YbRh2Si2 single crystals down to 30 mK. S(T) is found negative with comparably large values in the paramagnetic state. In zero field no Landau-Fermi-liquid (LFL) like behavior is observed within the magnetically ordered phase. However, a sign change from negative to positive appears at lowest temperatures on the magnetic side of the QCP. For higher fields B > Bc a linear extrapolation of S to zero clearly evidences the recovery of LFL regime. The crossover temperature is sharply determined and coincides perfectly with the one derived from resistivity and specific heat investigations.