Hexagonal warping control of exceptional points in topological insulator–ferromagnet heterojunctions

Abstract

Exceptional points (EPs) are non-Hermitian degeneracies, where both eigenvalues and eigenvectors coalesce, which are fundamentally distinct from their Hermitian counterparts. In this study, we investigate the influence of hexagonal warping on EPs emerging at the interfaces between topological insulators and ferromagnets. We demonstrate that the presence of the warping term plays a crucial role in determining the locations of the EPs. Furthermore, we show that the number as well as the positions of EPs emerging at such junctions can be tuned by an applied magnetic field. Our results, in line with previous studies on topological insulator–ferromagnet junctions, suggest them as a promising platform for realizing non-Hermitian physics.