The thermopower as a fingerprint of the Kondo breakdown quantum critical point

TL;DR

This paper suggests that thermopower measurements can distinguish between two competing theories of quantum criticality in heavy fermions, highlighting a collapse in the Seebeck coefficient as a key signature of Kondo breakdown.

Contribution

It introduces thermopower as a diagnostic tool to differentiate Kondo breakdown from SDW quantum critical scenarios in heavy fermion systems.

Findings

Seebeck coefficient collapses at the energy scale $E^{*}$ in Kondo breakdown.

Experimental data for YbRh$_2$Si$_2$ supports the Kondo breakdown scenario.

Thermopower behavior differs fundamentally between the two theories.

Abstract

We propose that the thermoelectric power distinguishes two competing scenarios for quantum phase transitions in heavy fermions : the spin-density-wave (SDW) theory and breakdown of the Kondo effect. In the Kondo breakdown scenario, the Seebeck coefficient turns out to collapse from the temperature scale $E^{*}$, associated with quantum fluctuations of the Fermi surface reconfiguration. This feature differs radically from the physics of the SDW theory, where no reconstruction of the Fermi surface occurs, and can be considered as the hallmark of the Kondo breakdown theory. We test these ideas, upon experimental results for YbRh$_2$Si$_2$.