Magnetic-field switchable metal-insulator transitions in a quasi-helical conductor

TL;DR

This paper investigates how magnetic fields can switch a quasi-helical conductor between localized and delocalized states by tuning spin overlaps, revealing two distinct localization transitions in disordered systems.

Contribution

It introduces a unified two-step renormalization group method to analyze magnetic-field-induced localization transitions in quasi-helical conductors.

Findings

Identification of two localization transitions with increasing magnetic field.

Demonstration that disorder backscattering enables localization despite spin-momentum locking.

Analysis of how spin-wavefunction overlap influences localization behavior.

Abstract

We study Anderson localization in disordered helical conductors that are obtained from one-dimensional conductors with spin-orbit interaction and a magnetic field, or from equivalent systems. We call such conductors "quasi-helical" because the spins of the counterpropagating modes are not perfectly antiparallel and have a small spin-wavefunction overlap that is tunable by the magnetic field. Due to the overlap, disorder backscattering is possible and allows a localization transition. A conductor can pass through two localization transitions with increasing field, one from the conventionally localized system to the quasi-helical conductor (with localization length exceeding the system length), and one at a higher field again to a localized state, due now, however, to backscattering below the magnetic field induced pseudo-gap. We investigate these transitions using a unified two-step renormalization group approach.