Wilson Line and Disorder Invariants of Topological One-Dimensional Multiband Models

TL;DR

This paper introduces a Wilson line method to compute topological invariants in multiband 1D models, capturing all edge states and analyzing disorder effects, advancing the understanding of topological phases.

Contribution

The paper presents a novel Wilson line approach for efficiently calculating topological invariants in multiband 1D models, including models with many phases and overlooked edge states.

Findings

Wilson line accurately captures all topological edge states

Method applies to models with many topological phases

Disorder can protect or suppress edge states based on symmetry

Abstract

Topological invariants, such as the winding number, the Chern number, and the Zak phase, characterize the topological phases of bulk materials. Through the bulk-boundary correspondence, these topological phases have a one-to-one correspondence to topological edge states, which are robust to certain classes of disorder. For simple models like the Su-Schrieffer-Heeger (SSH) model, the computation of the winding number and Zak phase are straightforward, however, in multiband systems, this is no longer the case. In this work, we introduce the unwrapped Wilson line across the Brillouin zone to compute the bulk topological invariant. This method can efficiently be implemented numerically to evaluate multiband SSH-type models, including models that have a large number of distinct topological phases. This approach accurately captures all topological edge states, including those overlooked by traditional invariants, such as the winding number and Zak phase. To make a connection to experiments, we determine the sign of the topological invariant by considering a Hall-like configuration. We further introduce different classes of disorder that leave certain edge states protected, while suppressing other edge states, depending on their symmetry properties. Our approach is illustrated using different one-dimensional models, providing a robust framework for understanding topological properties in one-dimensional systems.