Singular charge fluctuations at a magnetic quantum critical point

TL;DR

This paper reports terahertz spectroscopy on YbRh₂Si₂ revealing frequency-over-temperature scaling of optical conductivity, indicating critical charge fluctuations are central to strange metal behavior and quantum criticality.

Contribution

It provides experimental evidence of critical charge fluctuations at a magnetic quantum critical point, advancing understanding of strange metal phenomena beyond traditional Landau theory.

Findings

Frequency-over-temperature scaling of optical conductivity observed

Critical charge fluctuations implicated in strange metal behavior

Evidence of beyond-Landau quantum criticality in YbRh₂Si₂

Abstract

Strange metal behavior is ubiquitous to correlated materials ranging from cuprate superconductors to bilayer graphene. There is increasing recognition that it arises from physics beyond the quantum fluctuations of a Landau order parameter which, in quantum critical heavy fermion antiferromagnets, may be realized as critical Kondo entanglement of spin and charge. The dynamics of the associated electronic delocalization transition could be ideally probed by optical conductivity, but experiments in the corresponding frequency and temperature ranges have remained elusive. We present terahertz time-domain transmission spectroscopy on molecular beam epitaxy-grown thin films of YbRh$_2$Si$_2$, a model strange metal compound. We observe frequency over temperature scaling of the optical conductivity as a hallmark of beyond-Landau quantum criticality. Our discovery implicates critical charge fluctuations as playing a central role in the strange metal behavior, thereby elucidating one of the longstanding mysteries of correlated quantum matter.