Observation of a Critical Charge Mode in a Strange Metal

TL;DR

This study uses advanced Mossbauer spectroscopy to directly observe critical charge fluctuations in a strange metal, revealing a new signature of its unconventional electronic behavior near localization.

Contribution

It provides the first direct evidence of critical charge fluctuations in a strange metal using synchrotron-radiation-based Mossbauer spectroscopy.

Findings

Observation of peak splitting indicating charge fluctuations

Detection of long time-scale valence fluctuations

Evidence of charged polaron formation

Abstract

Quantum electronic matter has long been understood in terms of two limiting behaviors of electrons: one of delocalized metallic states, and the other of localized magnetic states. Understanding the strange metallic behavior which develops at the brink of localization demands new probes of the underlying electronic charge dynamics. Using a state-of-the-art technique, synchrotron-radiation-based Mossbauer spectroscopy, we have studied the longitudinal charge fluctuations of the strange metal phase of beta-YbAlB4 as a function of temperature and pressure. We find that the usual single absorption peak in the Fermi-liquid regime splits into two peaks upon entering the critical regime. This spectrum is naturally interpreted as a single nuclear transition, modulated by nearby electronic valence fluctuations whose long time-scales are further enhanced, due to the formation of charged polarons. Our results represent a direct observation of critical charge fluctuations as a new signature of strange metals.