Second-order topological non-Hermitian skin effects

TL;DR

This paper introduces a new class of non-Hermitian skin effects arising from second-order topology, with modes localized at corners, expanding the understanding of topological phenomena in non-Hermitian systems.

Contribution

It proposes the concept of second-order topological skin effects in non-Hermitian systems, demonstrating intrinsic and extrinsic types linked to second-order topology and symmetry considerations.

Findings

Skin modes are localized at corners in 2D systems.

Intrinsic effects are characterized by bulk inversion and chiral symmetry.

Extrinsic effects relate edge-topology to corner localization.

Abstract

Higher-order topology realizes topologically robust corner modes as a manifestation of nontriviality. We theoretically propose non-Hermitian skin effects which stem from second-order topology of chiral-symmetric Hermitian systems. It is found that the skin modes are localized at the corners. We demonstrate two types of second-order topological skin effects by two-dimensional intrinsic and extrinsic second-order topology. The intrinsic second-order topological skin effect is characterized topologically by bulk inversion symmetry as well as chiral symmetry. Meanwhile, the extrinsic second-order topological skin effect occurs from the topological correspondence between the edges and corners. We show that the non-Hermitian skin modes emerge by using a relationship between second-order and conventional first-order topology.