Interferences Measure Topology

TL;DR

This paper introduces a universal method to directly measure topological invariants in materials by analyzing local electronic density patterns, facilitating the identification of topological states for quantum technology applications.

Contribution

It presents a novel approach linking local electronic density to topological invariants via Atiyah Singer index theorems, enabling direct detection of topological states.

Findings

Method allows direct measurement of winding number

Detects topological defects through density interference patterns

Provides a practical route to identify topological materials

Abstract

Topological materials are characterized by integer invariants that underpin their robust quantized electronic features, as famously exemplified by the Chern number in the integer quantum Hall effect. Yet, in most candidate systems, the observable linked to the topological invariant is unknown, preventing direct verification of their topological nature. Here we present a general method to identify topological materials by analyzing the local electronic density, $\delta \rho(\boldsymbol{r})$, and connecting it to Atiyah Singer index theorems. This approach enables a direct measurement of the winding number, the topological invariant of Hamiltonians with chiral symmetry, through a contour independent dislocation pattern of $\delta \rho(\boldsymbol{r})$ created by interference from topological defects. Our method thus provides a direct route to detect and characterize quantum topological states, paving the way for their use as robust and entangleable building blocks in quantum technologies.