Non-Hermitian higher-order topological insulators enabled by altermagnet engineering

TL;DR

This paper demonstrates how altermagnet proximity can induce non-Hermitian higher-order topological phases, enabling control over edge and corner states through spectral winding and magnetic tuning.

Contribution

It introduces altermagnet engineering as a novel method to realize and manipulate non-Hermitian higher-order topological insulators with controllable skin and topological effects.

Findings

Proximity to altermagnets gaps edge states, inducing a topological phase transition.

Nonreciprocal hopping leads to skin and hybrid skin-topological effects.

Spectral winding number controls corner localization and can be reversed by tuning altermagnetic order.

Abstract

We show that proximity to an altermagnet provides an efficient route to engineering non-Hermitian higher-order topological phases. The proximity-induced altermagnetic order gaps the edge states of a topological insulator, thereby driving a transition from a first-order to a second-order topological phase. When combined with nonreciprocal hopping, the system exhibits both the non-Hermitian skin effect and a hybrid skin-topological effect, whereby first-order edge states and second-order corner states accumulate at selected corners of the lattice. We demonstrate that the spectral winding number of the edge states under cylindrical geometry dictates this corner localization and can be reversed by tuning the altermagnetic order. Consequently, both edge and corner states become directionally controllable. Our results establish altermagnets as a versatile platform for realizing and tuning skin-topological phenomena in non-Hermitian higher-order topological systems.