Transport anisotropy in Ge quantum wells in the absence of quantum oscillations

TL;DR

This study shows that transport anisotropy in Ge quantum wells persists at high temperatures without quantum oscillations, indicating a different origin than stripe phases or known effects like surface roughness.

Contribution

It demonstrates that transport anisotropy in Ge quantum wells exists independently of quantum oscillations and rules out stripe phases as its cause.

Findings

Anisotropy persists at high temperatures and filling factors.

Quantum oscillations are not necessary for anisotropy.

Stripe phases are unlikely to be the cause.

Abstract

Recent study of a high-mobility 2D hole gas in a strained Ge quantum well revealed strong transport anisotropy in the quantum Hall regime when the magnetic field was tilted away from the sample normal. In the present study we demonstrate that the anisotropy persists to such high temperatures and filling factors that quantum oscillations are no longer observed. This finding rules out the formation of a stripe phase as a possible origin for the observed anisotropy. However, we also show that the observed anisotropy is not consistent with other known anisotropies, such as those arising from finite thickness effects or surface roughness.