Quantum Valence Criticality as Origin of Unconventional Critical Phenomena

TL;DR

This paper explains unconventional critical phenomena in certain paramagnetic metals through quantum criticality of Yb-valence fluctuations, unifying various low-temperature anomalies with a mode coupling theory.

Contribution

It introduces a mode coupling theory incorporating local correlation effects to explain the quantum criticality of Yb-valence fluctuations and associated phenomena.

Findings

Unconventional criticality arises from locality of valence fluctuation mode.

Divergence of spin susceptibility and Wilson ratio enhancement explained.

T-linear resistivity emerges from valence fluctuation quantum criticality.

Abstract

It is shown that unconventional critical phenomena commonly observed in paramagnetic metals YbRh2Si2, YbRh2(Si0.95Ge0.05)2, and beta-YbAlB4 is naturally explained by the quantum criticality of Yb-valence fluctuations. We construct the mode coupling theory taking account of local correlation effects of f electrons and find that unconventional criticality is caused by the locality of the valence fluctuation mode. We show that measured low-temperature anomalies such as divergence of uniform spin susceptibility $\chi T^{-\zeta)$ with $\zeta~0.6$ giving rise to a huge enhancement of the Wilson ratio and the emergence of T-linear resistivity are explained in a unified way.