Giant Anisotropic Magnetoresistance in a Quantum Anomalous Hall Insulator

TL;DR

This paper investigates how the edge states in a quantum anomalous Hall insulator evolve with magnetization direction, revealing a giant, tunable anisotropic magnetoresistance that helps quantify edge contributions to transport.

Contribution

It demonstrates a field-tilt driven crossover from edge state to diffusive transport in a topological insulator, introducing a method to quantify edge state contributions using Landauer-Buttiker formalism.

Findings

Giant anisotropic magnetoresistance observed during the edge-to-diffusive transport transition.

Electrical tunability of magnetoresistance linked to magnetization orientation.

Method enables analysis of edge state transport away from perfect quantization.

Abstract

When a three-dimensional (3D) ferromagnetic topological insulator thin film is magnetized out-of-plane, conduction ideally occurs through dissipationless, one-dimensional (1D) chiral states that are characterized by a quantized, zero-field Hall conductance. The recent realization of this phenomenon - the quantum anomalous Hall effect - provides a conceptually new platform for studies of edge-state transport, distinct from the more extensively studied integer and fractional quantum Hall effects that arise from Landau level formation. An important question arises in this context: how do these 1D edge states evolve as the magnetization is changed from out-of-plane to in-plane? We examine this question by studying the field-tilt driven crossover from predominantly edge state transport to diffusive transport in Cr-doped (Bi,Sb)2Te3 thin films, as the system transitions from a quantum anomalous Hall insulator to a gapless, ferromagnetic topological insulator. The crossover manifests itself in a giant, electrically tunable anisotropic magnetoresistance that we explain using the Landauer-Buttiker formalism. Our methodology provides a powerful means of quantifying edge state contributions to transport in temperature and chemical potential regimes far from perfect quantization.