Skin-topological effect in two-dimensional nonreciprocal topological superconductor

TL;DR

This paper explores how non-Hermitian skin effects influence topological edge states in two-dimensional superconductors with different types of non-reciprocity, revealing symmetry-protected localization phenomena and tunable edge states.

Contribution

It introduces a comprehensive analysis of skin-topological effects in 2D nonreciprocal topological superconductors considering both spin-independent and spin-dependent non-Hermitian terms, highlighting symmetry protections and external field control.

Findings

Spin-independent non-reciprocal hopping leads to corner localization protected by PHS.

Spin-dependent non-reciprocal hopping results in Kramers doublets localized at opposite corners protected by TRS.

External magnetic fields can eliminate NHSE in the spectrum continuum while preserving effects on zero-energy states.

Abstract

We investigate the interplay between non-Hermitian skin effect (NHSE) and topological properties in two-dimensional topological superconductor. Two kinds of non-Hermiticity are considered. The first is the spin-independent non-reciprocal hopping, which respects particle-hole symmetry (PHS) and dictates the bulk as well as topological edge modes localize at opposite corners, manifested as the $Z_2$ NHSE protected by PHS. The direction of the localization can be conveniently characterized by the sign of the winding numbers. The other is the spin-dependent non-reciprocal hopping, where the NHSE is protected by time-reversal symmetry (TRS). The Kramers doublets are localized at opposite corners, namely the TRS protected $Z_2$ NHSE. When apply an external magnetic field, its internal symmetry changes from the symplectic class into the orthogonal class, eliminating the NHSE for the states in the spectrum continuum. For the zero energy states which are isolated, the NHSE still has its effects despite the orthogonality. For the spin-independent case, edge states can be effectively tuned by the direction of Zeeman field, where at certain directions the zero-energy edge state can be free of NHSE and uniformly distributed. Our work paves the way for the study of the interplay between topology and non-Hermiticity in superconducting systems.