Anderson localization at the boundary of a two-dimensional topological superconductor

TL;DR

This paper investigates how topologically protected modes influence Anderson localization in 2D topological superconductor boundaries, revealing the crossover from diffusive to localized regimes and extending understanding of topological effects on transport.

Contribution

It introduces a non-perturbative sigma-model approach to analyze transport in class D topological superconducting wires with protected modes, including the effects of topological terms.

Findings

Protected modes alter conductance and noise characteristics.

The formalism captures the crossover from diffusive to localized regimes.

Topological terms lead to additional eigenstates affecting localization.

Abstract

A one-dimensional boundary of a two-dimensional topological superconductor can host a number of topologically protected chiral modes. Combining two topological superconductors with different topological indices, it is possible to achieve a situation when only a given number of channels ($m$) are topologically protected, while others are not and therefore are subject to Anderson localization in the presence of disorder. We study transport properties of such quasi-one-dimensional quantum wires with broken time-reversal and spin-rotational symmetries (class D) and calculate the average conductance, its variance and the third cumulant, as well as the average shot noise power. The results are obtained for arbitrary wire length, tracing a crossover from the diffusive Drude regime to the regime of strong localization where only $m$ protected channels conduct. Our approach is based on the non-perturbative treatment of the non-linear supersymmetric sigma model of symmetry class D with two replicas developed in our recent publication [D. S. Antonenko et al., Phys. Rev. B 102, 195152 (2020)]. The presence of topologically protected modes results in the appearance of a topological Wess-Zumino-Witten term in the sigma-model action, which leads to an additional subsidiary series of eigenstates of the transfer-matrix Hamiltonian. The developed formalism can be applied to study the interplay of Anderson localization and topological protection in quantum wires of other symmetry classes.