Giant universal conductance fluctuations in the antiferromagnetic topological insulator MnBi2Te4

TL;DR

This paper reports the observation of giant universal conductance fluctuations in mesoscopic MnBi2Te4, revealing long phase coherence lengths and highlighting the potential for quantum spin interferometry in magnetic topological insulators.

Contribution

It demonstrates the longest phase-coherence length in a magnetic topological insulator and characterizes conductance fluctuations, advancing understanding of quantum interference in these materials.

Findings

Longest phase-coherence length (~500nm at 1K) observed in MnBi2Te4.

Giant conductance fluctuations (~20e2/h) due to quantum interference.

Identification of dephasing mechanisms related to magnetism and magnetic flux.

Abstract

Intrinsic magnetic topological insulators can host quantum states with quantized magneto-electric responses, such as the axion and Chern insulators states evidenced in ultra-thin MnBi2Te4 films. Yet, whereas quantization is investigated thoroughly, transport properties related to the phase of charge carriers remains unexplored. Here, we study quantum coherent transport in mesoscopic Hall bars fabricated from thick exfoliated MnBi2Te4 flakes, and reveal the longest phase-coherence length ever observed in a mesoscopic magnet (about 500nm at 1K), associated to 2D topological surface states. In the fully-coherent regime, significant non-local contributions to quantum interference up to the micron scale lead to giant-amplitude universal conductance fluctuations (about 20e2/h). In the self-averaging regime, the statistical properties of conductance fluctuations confirm the 2D nature of quantum interference and different dephasing mechanisms are identified, as due to either magnetism or magnetic flux through coherent loops. Remarkably, the weak decoherence in magnetic topological insulator nanostructures show their potential to realize novel quantum spin interferometers based on dephasing by local magnetic textures at liquid-helium temperatures.