Singular charge fluctuations at a magnetic quantum critical point.

Prochaska, L; Li, X; MacFarland, D C; Andrews, A M; Bonta, M; Bianco, E F; Yazdi, S; Schrenk, W et al. · Science · 2020

basic_science · Level V

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Abstract

Strange metal behavior is ubiquitous in correlated materials, ranging from cuprate superconductors to bilayer graphene, and may arise from physics beyond the quantum fluctuations of a Landau order parameter. In quantum-critical heavy-fermion antiferromagnets, such physics may be realized as critical Kondo entanglement of spin and charge and probed with optical conductivity. We present terahertz time-domain transmission spectroscopy on molecular beam epitaxy-grown thin films of YbRh<sub>2</sub>Si<sub>2</sub>, a model strange-metal compound. We observed frequency over temperature scaling of the optical conductivity as a hallmark of beyond-Landau quantum criticality. Our discovery suggests that critical charge fluctuations play a central role in the strange metal behavior, elucidating one of the long-standing mysteries of correlated quantum matter.