Multivalley two-dimensional electron system in an AlAs quantum well with mobility exceeding $2\times10^6$ cm$^{2}$V$^{-1}$s$^{-1}$

TL;DR

This paper reports the creation of ultra-high mobility multivalley 2D electron systems in AlAs quantum wells, enabling advanced studies of quantum Hall effects and valleytronics with significantly improved sample quality.

Contribution

The study demonstrates electron mobilities exceeding 2 million cm^2/Vs in AlAs quantum wells, a tenfold improvement over previous results, and observes high-order fractional quantum Hall states.

Findings

Electron mobility peaks at 2.4×10^6 cm^2/Vs.

Observation of fractional quantum Hall minima up to ν=8/17.

Detection of the elusive ν=1/5 quantum Hall state.

Abstract

Degenerate conduction-band minima, or `valleys', in materials such as Si, AlAs, graphene, and MoS$_2$ allow them to host two-dimensional electron systems (2DESs) that can access a valley degree of freedom. These multivalley 2DESs present exciting opportunities for both pragmatic and fundamental research alike because not only are they a platform for valleytronic devices, but they also provide a tool to tune and investigate the properties of complex many-body ground states. Here, we report ultra-high quality, modulation doped AlAs quantum wells containing 2DESs that occupy two anisotropic valleys and have electron mobilities peaking at $2.4\times10^6$ cm$^{2}$V$^{-1}$s$^{-1}$ at a density of $2.2\times10^{11}$ cm$^{-2}$. This is more than an order of magnitude improvement in mobility over previous results. The unprecedented quality of our samples is demonstrated by magneto-transport data that show high-order fractional quantum Hall minima up to the Landau level filling $\nu=8/17$, and even the elusive $\nu=1/5$ quantum Hall state.