Universal Conductance Fluctuations of Topological Insulators

TL;DR

This review discusses the universal conductance fluctuations in topological insulators, highlighting their topological nature, symmetry properties, and experimental observations, which are crucial for future quantum device applications.

Contribution

The paper provides a comprehensive overview of the topological nature of UCF in TIs, including experimental evidence and symmetry analysis, advancing understanding of quantum transport in these materials.

Findings

Demonstration of 2D UCF in TIs with topological origin

Observation of symmetry-driven changes in UCF amplitude

Reconciliation of experimental results with theoretical models

Abstract

As an exotic quantum condensed matter, the topological insulator (TI) is a bulk-insulating material with a Dirac-type conducting surface state. Such dissipationless transport of topological surface states (TSSs) is protected by the time-reversal symmetry, which leads to the potential applications in spintronics and quantum computations. Understanding the topological symplectic transport of the Dirac fermions is a key issue to study and design the TI-based devices. In this review, we introduce the progress on the universal conductance fluctuation (UCF) of TSSs. Firstly, we report the two dimensional UCF phenomenon in TIs, and its topological nature is demonstrated based on the investigations of UCF by angle-varying, in-plane field tuning and scaling analysis. Secondly, we discuss the statistical symmetry of UCF in TIs. For a single TSS, the applied magnetic field will drive the system from a Gaussian symplectic ensemble into a Gaussian unitary ensemble. It results a 2^0.5 fold increase of the UCF amplitude. However, the experiment reveals a decreasing of the UCF amplitude of 2^0.5 times. This is contradictory to the theoretical prediction. Actually, there are two TSSs and they are coherently coupled to each other in TIs since the sample's thickness is shorter than its bulk dephasing length. This leads to a Gaussian orthogonal ensemble of the interface coupling system without an external field. In such situation, the UCF amplitude will decrease by 2^0.5 times with the field increasing. It is consistent with the experimental results. Finally, the other progress on UCFs is also discussed.