Exciton Condensation and Perfect Coulomb Drag

TL;DR

This paper demonstrates perfect Coulomb drag in a bilayer electron system with an exciton condensate, where a current in one layer induces an equal and opposite current in the other, highlighting strong electron-hole correlations.

Contribution

The study provides experimental evidence of perfect Coulomb drag driven by exciton condensation, with negligible tunneling between layers, advancing understanding of correlated electron systems.

Findings

Demonstration of perfect Coulomb drag in bilayer systems

Evidence of electron-hole pairing dominating transport

Negligible charge tunneling between layers

Abstract

Coulomb drag is a process whereby the repulsive interactions between electrons in spatially separated conductors enable a current flowing in one of the conductors to induce a voltage drop in the other. If the second conductor is part of a closed circuit, a net current will flow in that circuit. The drag current is typically much smaller than the drive current owing to the heavy screening of the Coulomb interaction. There are, however, rare situations in which strong electronic correlations exist between the two conductors. For example, bilayer two-dimensional electron systems can support an exciton condensate consisting of electrons in one layer tightly bound to holes in the other. One thus expects "perfect" drag; a transport current of electrons driven through one layer is accompanied by an equal one of holes in the other. (The electrical currents are therefore opposite in sign.) Here we demonstrate just this effect, taking care to ensure that the electron-hole pairs dominate the transport and that tunneling of charge between the layers is negligible.