Fingerprints of quantum criticality in locally resolved transport

TL;DR

This paper proposes using local imaging techniques to detect quantum critical signatures in transport properties of strange metals, supported by holographic models and experimental comparisons, to better understand Planckian resistivity.

Contribution

It introduces a holographic model predicting local transport signatures of quantum criticality and suggests local imaging as a tool to explore universality in strange metals.

Findings

Quantitative agreement with graphene transport data

Prediction of local current flow signatures of quantum criticality

Proposal for experimental tests of universality in T-linear resistivity

Abstract

Understanding electrical transport in strange metals, including the seeming universality of Planckian $T$-linear resistivity, remains a longstanding challenge in condensed matter physics. We propose that local imaging techniques, such as nitrogen vacancy center magnetometry, can locally identify signatures of quantum critical response which are invisible in measurements of a bulk electrical resistivity. As an illustrative example, we use a minimal holographic model for a strange metal in two spatial dimensions to predict how electrical current will flow in regimes dominated by quantum critical dynamics on the Planckian length scale. We describe the crossover between quantum critical transport and hydrodynamic transport (including Ohmic regimes), both in charge neutral and finite density systems. We compare our holographic predictions to experiments on charge neutral graphene, finding quantitative agreement with available data; we suggest further experiments which may determine the relevance of our framework to transport on Planckian scales in this material. More broadly, we propose that locally imaged transport be used to test the universality (or lack thereof) of microscopic dynamics in the diverse set of quantum materials exhibiting $T$-linear resistivity.