A complete laboratory for transport studies of electron-hole interactions in GaAs/AlGaAs systems

TL;DR

This paper introduces GaAs/AlGaAs double quantum well devices capable of studying electron-hole and hole-hole interactions, revealing signs of exciton condensation in magnetic fields and strong Coulomb drag at low temperatures.

Contribution

It demonstrates a versatile device platform for investigating electron-hole and hole-hole bilayer interactions with narrow barriers, including observations of exciton condensation and Coulomb drag effects.

Findings

Signs of magnetic-field-induced exciton condensation in h-h bilayers.

Strong Coulomb drag resistivity observed at low temperatures.

No definitive exciton condensation observed in e-h bilayers.

Abstract

We present GaAs/AlGaAs double quantum well devices that can operate as both electron-hole (e-h) and hole-hole (h-h) bilayers, with separating barriers as narrow as 5 nm or 7.5 nm. With such narrow barriers, in the h-h configuration we observe signs of magnetic-field-induced exciton condensation in the quantum Hall bilayer regime. In the same devices we can study the zero-magnetic-field e-h and h-h bilayer states using Coulomb drag. Very strong e-h Coulomb drag resistivity (up to 10% of the single layer resistivity) is observed at liquid helium temperatures, but no definite signs of exciton condensation are seen in this case. Self-consistent calculations of the electron and hole wavefunctions show this might be because the average interlayer separation is larger in the e-h case than the h-h case.