Record-quality GaAs two-dimensional hole systems

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 ×10⁶cm² /(V s) at a hole density of p =1.3 ×10¹¹ /cm², implying a mean free path of ≃27 μ m . In the low-temperature magnetoresistance trace of this sample, we observe high-order fractional quantum Hall states up to the Landau level filling ν =12 /25 near ν =1 /2 . Furthermore, we see a deep minimum develop at ν =1 /5 in the magnetoresistance of a sample with a much lower hole density of p =4.0 ×10¹⁰ /cm² where we measure a mobility of 3.6 ×10⁶cm² /(V s). These improvements in sample quality were achieved by the reduction of residual impurities both in the GaAs channel and in the AlGaAs barrier material, as well as optimization in the design of the sample structure.