Dependence of persistent gaps at Landau level crossings on relative spin

TL;DR

This study investigates how the energy gaps at Landau level crossings in AlAs quantum wells depend on magnetic field and the relative spin orientation, revealing an unexpected spin-dependent behavior.

Contribution

It uncovers a novel spin-dependent dependence of quantum Hall gaps at Landau level crossings, which was not previously understood.

Findings

Gaps increase approximately linearly with magnetic field.

Parallel-spin crossings have larger gaps than antiparallel-spin crossings.

The dependence on spin orientation is an unexpected and significant result.

Abstract

We report measurements of the quantum Hall state energy gap at avoided crossings between Landau levels originating from different conduction band valleys in AlAs quantum wells. These gaps exhibit an approximately linear dependence on magnetic field over a wide range of fields and filling factors. More remarkably, we observe an unexpected dependence of the gap size on the relative spin orientation of the crossing levels, with parallel-spin crossings exhibiting larger gaps than antiparallel-spin crossings.