# Topological chiral-gain in a Berry dipole material

## TL;DR

This paper explores how electric bias in a material can create chiral gain and topological edge states, enabling new photonic applications like unidirectional light propagation.

## Contribution

The paper reveals the topological origin of chiral gain and shows how it can be used to create boundary-confined lasing modes with controlled orbital angular momentum.

## Key findings

- Static electric bias induces topological bandgaps with unidirectional edge states.
- Chiral gain can be used to engineer lasing modes with orbital angular momentum locked to the electric field orientation.
- The results enable lossless edge-wave propagation and structured light generation.

## Abstract

Recent studies have shown that low-symmetry conductors under static electric bias offer a pathway to realize chiral gain, where the non-Hermitian optical response of the material is controlled by the spin angular momentum of the wave. In this work, we uncover the topological nature of chiral gain and demonstrate how a static electric bias induces topological bandgaps that support unidirectional edge states at the material boundaries. In our system, these topological edge states consistently exhibit dissipative properties. However, we show that, by operating outside the topological gap, the chiral gain can be leveraged to engineer boundary-confined lasing modes with orbital angular momentum locked to the orientation of the applied electric field. Our results open new possibilities for loss-compensated photonic waveguides, enabling advanced functionalities such as unidirectional, lossless edge-wave propagation and the generation of structured light with intrinsic orbital angular momentum.