Uncovering Exceptional Contours in non-Hermitian Hyperbolic Matter

TL;DR

This paper explores non-Hermitian hyperbolic lattices, revealing tunable exceptional points and contours, higher-order degeneracies, and boundary phenomena, advancing understanding of novel phases in hyperbolic matter with non-Hermitian effects.

Contribution

It introduces non-Hermitian hyperbolic matter, analyzing its exceptional properties and band structures using hyperbolic Bloch theory and numerical methods, highlighting new degeneracies and boundary effects.

Findings

Accessible and tunable exceptional points in {10,5} tessellations

Higher-order exceptional points in {8,4} tessellations

Boundary localization and spectra analysis

Abstract

Hyperbolic lattices are starting to be explored in search of novel phases of matter. At the same time, non-Hermitian physics has come to the forefront in photonic, optical, phononic, and condensed matter systems. In this work, we introduce non-Hermitian hyperbolic matter and elucidate its exceptional properties in depth. We use hyperbolic Bloch theory to investigate band structures of hyperbolic lattices in the presence of non-Hermitian on-site gain and loss as well as non-reciprocal hopping. Using various analytical and numerical approaches we demonstrate widely accessible and tunable exceptional points and contours in {10,5} tessellations, which we characterize using phase rigidity, energy scaling, and vorticity. We further demonstrate the occurrence of higher-order exceptional points and contours in the {8,4} tessellations using the method of Newton polygons, supported by vorticity and phase rigidity computations. Finally, we investigate the open boundary spectra and densities of states to compare with results from band theory, along with a demonstration of boundary localisation. Our results unveil an abundance of exceptional degeneracies in hyperbolic non-Hermitian matter.