The thermopower as a signature of quantum criticality in heavy fermions

TL;DR

This paper proposes using the Seebeck coefficient as a diagnostic tool to identify the nature of quantum critical points in heavy fermion materials, distinguishing between Kondo breakdown and SDW scenarios through characteristic signatures.

Contribution

It introduces a novel experimental approach using thermopower measurements to differentiate types of quantum criticality in heavy fermion compounds.

Findings

Seebeck coefficient collapses at Kondo breakdown QCP

Symmetric Seebeck behavior around SDW QCP

Potential sign change of Seebeck coefficient at QCP

Abstract

We present a series of arguments showing that the Seebeck coefficient can be used as a decisive experiment to characterize the nature of the quantum critical point (QCP) in heavy fermion compounds. Being reactive almost exclusively to the presence of delocalized entropic carriers, the Seebeck coefficient shows a drastic collapse at the Kondo breakdown QCP, as the reconstruction of the Fermi surface takes place. In contrast, around a Spin Density Wave (SDW) QCP, the Seebeck coefficient is broadly symmetric. We discuss the possibility of a change of sign at the QCP, the characteristic variation of $| S / T | $ with temperature and external parameter, as well as the capacity of the Seebeck coefficient to distinguish between localized and itinerant anti-ferromagnetism (AF). Suggestions of experiments are given in the case of four non conventional compounds : YbRh$_2$Si$_2$, Ce(Mn)In$_5$, CeCu$_{6-x}$Au$_x$ and URu$_2$Si$_2$.