Multivalley two-dimensional electron system in an AlAs quantum well with mobility exceeding $2\times 10^6$ cm${}^2$V${}^{-1}$s${}^{-1}$

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 $2.4\times 10^6$ cm${}^2$V${}^{-1}$s${}^{-1}$ at a density of $2.2\times 10^{11}$ 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 $\hat{I}½=8/17$, and even the elusive $\hat{I}½=1/5$ quantum Hall state.

6 pages, 4 figures