Observation of the Dirac fluid and the breakdown of the Wiedemann-Franz law in graphene

TL;DR

This paper reports the experimental observation of the Dirac fluid in graphene, showing a significant breakdown of the Wiedemann-Franz law and enhanced thermal conductivity, indicating collective hydrodynamic behavior of electrons.

Contribution

First direct evidence of the Dirac fluid in graphene demonstrating collective electron behavior and deviation from Fermi liquid predictions.

Findings

Thermal conductivity exceeds Fermi liquid predictions by an order of magnitude.

Breakdown of the Wiedemann-Franz law observed in graphene.

Evidence of hydrodynamic electron flow in a quantum electronic fluid.

Abstract

Interactions between particles in quantum many-body systems can lead to collective behavior described by hydrodynamics. One such system is the electron-hole plasma in graphene near the charge neutrality point which can form a strongly coupled Dirac fluid. This charge neutral plasma of quasi-relativistic fermions is expected to exhibit a substantial enhancement of the thermal conductivity, due to decoupling of charge and heat currents within hydrodynamics. Employing high sensitivity Johnson noise thermometry, we report the breakdown of the Wiedemann-Franz law in graphene, with a thermal conductivity an order of magnitude larger than the value predicted by Fermi liquid theory. This result is a signature of the Dirac fluid, and constitutes direct evidence of collective motion in a quantum electronic fluid.