Large Universal Conductance Fluctuations in Magnetic Topological Insulator MnBi₂Te₄Nanostructures

The intrinsic magnetic topological insulator MnBi₂Te₄ has gained increasing attention as a potential platform to investigate exotic topological phases, such as the Quantum Anomalous Hall or the Axion Insulator states. However, intrinsic disorder (Mn/Bi intermixing, local non-collinear magnetic textures) brings some experimental challenges to realize such topological devices. Quantum coherent transport gives access to some microscopic parameters related to both structural and magnetic disorder, as well as to dephasing related the band structure. Here, we present a detailed study of quantum coherent transport in mesoscopic Hall bars fabricated from exfoliated MnBi₂Te₄ single-crystals. We evidence the giant-amplitude universal conductance fluctuations related to an unprecedented long phase coherence length L_φ for a mesoscopic magnet. By comparing different measurement configurations, we separate the different contributions to dephasing (magnetic flux, local spin textures, Berry phase). Moreover, we reveal the weak decoherence at higher temperatures, specific to magnetic topological insulators. These results reveal the potential of magnetic topological insulators to realize quantum interferometers based on dephasing by magnetism.