Fluidity onset in graphene

Denis A Bandurin,Alexey I Berdyugin,Andre K Geim,Irina V Grigorieva,Andrey V Shytov,Moshe Ben Shalom,Leonid S Levitov,Gregory Falkovich,Roshan Krishna Kumar

doi:10.1038/s41467-018-07004-4

Abstract

Viscous electron fluids have emerged recently as a new paradigm of strongly-correlated electron transport in solids. Here we report on a direct observation of the transition to this long-sought-for state of matter in a high-mobility electron system in graphene. Unexpectedly, the electron flow is found to be interaction-dominated but non-hydrodynamic (quasiballistic) in a wide temperature range, showing signatures of viscous flows only at relatively high temperatures. The transition between the two regimes is characterized by a sharp maximum of negative resistance, probed in proximity to the current injector. The resistance decreases as the system goes deeper into the hydrodynamic regime. In a perfect darkness-before-daybreak manner, the interaction-dominated negative response is strongest at the transition to the quasiballistic regime. Our work provides the first demonstration of how the viscous fluid behavior emerges in an interacting electron system.

Highlights

Viscous electron fluids have emerged recently as a new paradigm of strongly-correlated electron transport in solids
How does an electron system enter the fluid state? What happens when lee becomes comparable or larger than the system dimensions? What is the relation between electric current and potential at the transition? All these questions are at present poorly understood: neither there exists a detailed theory treating both ballistic and viscous electron regimes on equal footing, nor any systematic experimental study of the transition has been performed
Searching for the fluidity onset is the subject of this work

Summary

Introduction

Viscous electron fluids have emerged recently as a new paradigm of strongly-correlated electron transport in solids. Correspondence and requests for materials should be addressed to Electron fluids, an exotic state of matter in which electron–electron (ee) interactions dominate transport, have been long anticipated theoretically[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15] but until recently they were far from experimental reality. Lee in graphene can be varied over a wide range[23] by changing the carrier density n and T This enables a smooth transition (or, more precisely, a crossover) between single-particle ballistic and viscous transport regimes, allowing us to track how the electron system enters the collective fluid state. We will demonstrate that this transition can be conveniently quantified by the electron Knudsen number

Methods

Results

Conclusion