Ultra-high-quality GaAs and AlAs two-dimensional electron systems via molecular beam epitaxy

Tue, Jun 15, 2021, 10:30 am

Clean two-dimensional electron systems (2DESs) provide a near-scatter-free environment for electrons, making them useful for studying many branches of physics. This is particularly true for the investigation of delicate, interaction-driven quantum phenomena. Indeed, several many-body phases, such as Wigner solids, odd- and even-denominator fractional quantum Hall states (FQHSs), and stripe/nematic phases have materialized in 2DESs as sample quality progressed over time. Thus there is strong demand to achieve ever-higher-quality 2DESs, since there is potential to discover new intriguing physics.

In this talk, I will present a breakthrough in the quality of both AlAs and GaAs 2DESs and discuss how we achieved these results. Our new AlAs samples demonstrate mobility values that are ~8 times higher than the best earlier AlAs 2DESs. With such improvement in sample quality, we were even able to observe the elusive 𝜈 = 1/5 FQHS in AlAs. Previously, this fragile state had only ever been observed in the cleanest 2DESs, namely GaAs and graphene. Furthermore, our new GaAs 2DESs show mobility values that are significantly higher than former record-quality samples over a wide range of electron densities. We estimate only ~1 impurity for every 10 billion Ga/As atoms in our structures, and the impact of such cleanliness on many-body-electron phases is immediate. Several new FQHSs emerge, and we measure a remarkably large activation gap of Ξ”=820 mK for the 𝜈 = 5/2 FQHS, widely believed to be of non-Abelian nature. These results suggest an exciting future for further research concerning electron-electron interaction in a two-dimensional setting.