Scaling behavior of the thermopower of the archetypical heavy-fermion metal $\rm{YbRh_2Si_2}$

TL;DR

This paper investigates the scaling behavior of thermopower in heavy-fermion metal YbRh2Si2 under magnetic field, revealing universal features across different compounds and explaining anomalies at phase transitions through spectrum flattening.

Contribution

It demonstrates a universal scaling law for thermopower in heavy-fermion metals and explains its violation at phase transitions using spectrum flattening effects.

Findings

Scaling of S/T is universal among heavy-fermion compounds.

Thermopower exhibits two jumps and sign change at the antiferromagnetic transition.

Theoretical calculations agree with experimental data.

Abstract

We reveal and explain a scaling behavior of the thermopower $S/T$ exhibiting by the archetypical heavy-fermion (HF) metal $\rm{YbRh_2Si_2}$ under the application of magnetic field $B$ at temperatures $T$. We show that the same scaling is demonstrated by such different HF compounds as $\beta$-${\rm YbAlB_4}$ and the strongly correlated layered cobalt oxide $\rm [BiBa_{0.66}K_{0.36}O_{2}]CoO_{2}$. Using $\rm{YbRh_2Si_2}$ as an example, we demonstrate that the scaling behavior of $S/T$ is violated at the antiferromagnetic phase transition, while both the residual resistivity $\rho_0$ and the density of states $N$ experience jumps at the phase transition, making the thermopower experience two jumps and change its sign. Our elucidation is based on flattening of the single-particle spectrum that profoundly affects $\rho_0$ and $N$. To depict the main features of the $S/T$ behavior, we construct the $T-B$ schematic phase diagram of $\rm{YbRh_2Si_2}$. Our calculated $S/T$ for the HF compounds are in good agreement with experimental facts and support our observations.