Topological instabilities in ac-driven bosonic systems

TL;DR

This paper explores how topological properties influence dynamical instabilities in ac-driven bosonic systems, revealing a fundamental link and demonstrating boundary-localized, symmetry-protected instabilities.

Contribution

It establishes a general relation between topology and instability in non-equilibrium bosonic systems under ac-driving, introducing the concept of topological instabilities.

Findings

Localized instabilities occur at system boundaries.

Topological instabilities are symmetry protected.

A general relation between topology and instability is derived.

Abstract

Under non-equilibrium conditions, bosonic modes can become dynamically unstable with an exponentially growing occupation. On the other hand, topological band structures give rise to symmetry protected midgap states. In this letter, we investigate the interplay of instability and topology. Thereby, we establish a general relation between topology and instability under ac-driving. We apply our findings to create dynamical instabilities which are strongly localized at the boundaries of a finite-size system. As these localized instabilities are protected by symmetry, they can be considered as topological instabilities.