Experimental Progress towards Probing the Ground State of an Electron-Hole Bilayer by Low-Temperature Transport

K. Das Gupta,J. Waldie,H. E. Beere,D. A. Ritchie,A. F. Croxall,C. A. Nicoll,I. Farrer,M. Pepper

doi:10.1155/2011/727958

K. Das Gupta, J. Waldie + Show 6 more

Open Access

https://doi.org/10.1155/2011/727958

Copy DOI

Abstract

Recently, it has been possible to design independently contacted electron-hole bilayers (EHBLs) with carrier densities cm2in each layer and a separation of 10–20 nm in a GaAs/AlGaAs system. In these EHBLs, the interlayer interaction can be stronger than the intralayer interactions. Theoretical works have indicated the possibility of a very rich phase diagram in EHBLs consisting of excitonic superfluid phases, charge density waves, and Wigner crystals. Experiments have revealed that the Coulomb drag on the hole layer shows strong nonmonotonic deviations from a behaviour expected for Fermi-liquids at low temperatures. Simultaneously, an unexpected insulating behaviour in the single-layer resistances (at a highly “metallic” regime with ) also appears in both layers despite electron mobilities of above and hole mobilities over . Experimental data also indicates that the point of equal densities () is not special.

Highlights

Bringing two layers of 2-dimensional electron gases (2DEG) or a 2-dimensional hole gases (2DHG) in close proximity opens up possibilities that do not exist when the layers are very far apart
Features are seen in the drag resistivity at low temperatures that cannot be explained within the framework of Fermiliquid theory [41]
2x2DEGs, and 2x2DHGs in a magnetic field have shown striking evidence of transport by neutral objects driven by counterflow currents [33,34,35]

Summary

Introduction

Bringing two layers of 2-dimensional electron gases (2DEG) or a 2-dimensional hole gases (2DHG) in close proximity opens up possibilities that do not exist when the layers are very far apart. Let us recall that the ratio of the kinetic energy of a system of electrons and their potential energies due to mutual Coulomb interaction is measured by the parameter rs = Eee/E f (where Eee = e2 (πN )/4π 0 r and E f = π 2N/m∗ in 2-dimensions, with N electrons per unit area). Confining a large number of particles in a small area makes the interparticle spacing small and the Coulomb repulsion large, but the kinetic energy of the particles increases even faster—making rs smaller. This somewhat counterintuitive fact is a straightforward consequence of Fermi statistics and is true in all dimensions. Consider two parallel layers of electrons or holes with

Results

Discussion

Conclusion