Universal conductance fluctuations in a MnBi$_2$Te$_4$ thin film

TL;DR

This study investigates quantum coherence-driven conductance fluctuations in MnBi$_2$Te$_4$ thin films across different magnetic phases, revealing phase coherence lengths and magnetic domain effects on conductance fingerprints.

Contribution

It provides the first detailed analysis of universal conductance fluctuations in magnetic topological insulators, linking magnetic domain dynamics to quantum interference effects.

Findings

Charge carrier phase coherence length ~100 nm in all phases

Conductance fingerprints are reproducible within a phase but change across phase boundaries

Magnetofingerprint dependence on field sweep direction in antiferromagnetic phases

Abstract

Quantum coherence of electrons can produce striking behaviors in mesoscopic conductors, including weak localization and the Aharonov-Bohm effect. Although magnetic order can also strongly affect transport, the combination of coherence and magnetic order has been largely unexplored. Here, we examine quantum coherence-driven universal conductance fluctuations in the antiferromagnetic, canted antiferromagnetic, and ferromagnetic phases of a thin film of the topological material MnBi$_2$Te$_4$. In each magnetic phase we extract a charge carrier phase coherence length of about 100 nm. The conductance magnetofingerprint is repeatable when sweeping applied magnetic field within one magnetic phase, but changes when the applied magnetic field crosses the antiferromagnetic/canted antiferromagnetic magnetic phase boundary. Surprisingly, in the antiferromagnetic and canted antiferromagnetic phase, but not in the ferromagnetic phase, the magnetofingerprint depends on the direction of the field sweep. To explain these observations, we suggest that conductance fluctuation measurements are sensitive to the motion and nucleation of magnetic domain walls in MnBi$_2$Te$_4$.