Density imbalance effect on the Coulomb drag upturn in an electron-hole bialyer

TL;DR

This study investigates how density imbalance affects the low-temperature Coulomb drag upturn in an electron-hole bilayer, combining experimental measurements with numerical calculations to explore exciton-related phenomena.

Contribution

It provides new experimental data on drag behavior under density imbalance and compares it with theoretical models including pairing fluctuations.

Findings

Drag increases as either layer's density decreases.

Numerical models qualitatively reproduce the upturn but not the peak at matched densities.

Experimental results do not show the predicted peak at equal densities.

Abstract

A low-temperature upturn of the Coulomb drag resistivity measured in an undoped electron-hole bilayer (uEHBL) device, possibly manifesting from exciton formation or condensation, was recently observed. The effects of density imbalance on this upturn are examined. Measurements of drag as a function of temperature in a uEHBL with a 20 nm wide Al$_{.90}$Ga$_{.10}$As barrier layer at various density imbalances are presented. The results show drag increasing as the density of either two dimensional system was reduced, both within and above the upturn temperature regime. A comparison of the data with numerical calculations of drag in the presence of electron-hole pairing fluctuations, which qualitatively reproduce the drag upturn behavior, is also presented. The calculations, however, predict a peak in drag at matched densities, which is not reflected by the measurements.