Quantum Hall Exciton Condensation at Full Spin Polarization

TL;DR

This study investigates how Zeeman energy influences the excitonic phase transition in quantum Hall bilayers, revealing a non-monotonic critical layer separation and a broad transition region at high Zeeman energies.

Contribution

It provides new insights into the spin polarization effects on exciton condensation and introduces models involving mixed fluid phases to explain the observed phenomena.

Findings

Critical layer separation d/l initially increases then decreases with Zeeman energy.

Transition width broadens significantly at high Zeeman energies.

Excitonic and compressible phases are fully spin polarized at high Zeeman energies.

Abstract

Using Coulomb drag as a probe, we explore the excitonic phase transition in quantum Hall bilayers at nu=1 as a function of Zeeman energy, E_Z. The critical layer separation d/l for exciton condensation initially increases rapidly with E_Z, but then reaches a maximum and begins a gentle decline. At high E_Z, where both the excitonic phase at small d/l and the compressible phase at large d/l are fully spin polarized, we find that the width of the transition, as a function of d/l, is much larger than at small E_Z and persists in the limit of zero temperature. We discuss these results in the context of two models in which the system contains a mixture of the two fluids.