# Dynamic winding number for exploring band topology

## TL;DR

This paper introduces a dynamic winding number method to detect topological invariants in both Hermitian and non-Hermitian systems, overcoming challenges posed by exceptional points and enabling measurement through time-averaged observables.

## Contribution

It proposes a unified approach linking dynamic winding numbers to traditional topological invariants, applicable in one- and two-dimensional models.

## Key findings

- Dynamic winding number directly yields the conventional winding number in 1D.
- In 2D, the Chern number relates to the sum of dynamic winding numbers at phase singularities.
- Method allows measurement of topological invariants without prior knowledge of system topology.

## Abstract

Topological invariants play a key role in the characterization of topological states. Due to the existence of exceptional points, it is a great challenge to detect topological invariants in non-Hermitian systems. We put forward a dynamic winding number, the winding of realistic observables in long-time average, for exploring band topology in both Hermitian and non-Hermitian two-band models via a unified approach. We build a concrete relation between dynamic winding numbers and conventional topological invariants. In one-dimension, the dynamical winding number directly gives the conventional winding number. In two-dimension, the Chern number relates to the weighted sum of dynamic winding numbers of all phase singularity points. This work opens a new avenue to measure topological invariants not requesting any prior knowledge of system topology via time-averaged spin textures.