Quantum Hall Exciton Condensation at Full Spin Polarization

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.Comment: 4 pages, 3 eps figure

Quantum Hall Exciton Condensation at Full Spin Polarization

Using Coulomb drag as a probe, we explore the excitonic phase transition in quantum Hall bilayers at ν_T = 1 as a function of Zeeman energy E_Z. The critical layer separation (d/ℓ)_c 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

Exciton Transport and Andreev Reflection in a Bilayer Quantum Hall System

We demonstrate that counterflowing electrical currents can move through the bulk of the excitonic quantized Hall phase found in bilayer two-dimensional electron systems (2DES) even as charged excitations cannot. These counterflowing currents are transported by neutral excitons which are emitted and absorbed at the inner and outer boundaries of an annular 2DES via Andreev reflection