Non-Hermitian topological phase transitions in superlattices and the optical Dirac equation

TL;DR

This paper investigates topological phase transitions in optical superlattices with synthetic imaginary gauge fields, revealing a universal non-Hermitian Dirac equation description and demonstrating a photonic system exhibiting such transitions.

Contribution

It introduces a novel topological phase transition in optical superlattices described by a non-Hermitian Dirac equation with Lorentz-symmetry violation.

Findings

Topological phase transition characterized by spectral winding number change

Universal form of phase transition described by non-Hermitian Dirac equation

Photonic system based on light coupling in co-propagating gratings demonstrating the transition

Abstract

Optical superlattices with sublattice symmetry subjected to a synthetic imaginary gauge field undergo a topological phase transition in the Bloch energy spectrum, characterized by the change of a spectral winding number. For a narrow gap, the phase transition is of universal form and described by a non-Hermitian Dirac equation with Lorentz-symmetry violation. A simple photonic system displaying such a phase transition is discussed, which is based on light coupling in co-propagating gratings.