Record-quality GaAs two-dimensional hole systems

TL;DR

This paper reports the creation of ultra-high-quality GaAs 2D hole systems with record mobilities, enabling observation of complex quantum Hall states and deepening understanding of many-body physics in these materials.

Contribution

The study demonstrates significant improvements in GaAs 2D hole system quality through refined fabrication, revealing high-order fractional quantum Hall states and deep minima at specific filling factors.

Findings

Record high mobility of 5.8×10^6 cm^2/Vs at high hole density

Observation of fractional quantum Hall states up to ν=12/25

Deep minimum at ν=1/5 indicating strong many-body effects

Abstract

The complex band structure, large spin-orbit induced band splitting, and heavy effective mass of two-dimensional (2D) hole systems hosted in GaAs quantum wells render them rich platforms to study many-body physics and ballistic transport phenomena. Here we report ultra-high-quality (001) GaAs 2D hole systems, fabricated using molecular beam epitaxy and modulation doping, with mobility values as high as $5.8\times10^6$ cm$^2$/Vs at a hole density of $p=1.3\times10^{11}$ /cm$^2$, implying a mean-free path of $\simeq27$ $\mu$m. In the low-temperature magnetoresistance trace of this sample, we observe high-order fractional quantum Hall states up to the Landau level filling $\nu=12/25$ near $\nu=1/2$. Furthermore, we see a deep minimum develop at $\nu=1/5$ in the magnetoresistance of a sample with a much lower hole density of $p=4.0\times10^{10}$ /cm$^2$ where we measure a mobility of $3.6\times10^6$ cm$^2$/Vs. These improvements in sample quality were achieved by reduction of residual impurities both in the GaAs channel and the AlGaAs barrier material, as well as optimization in design of the sample structure.