Skin-topological effect in two-dimensional nonreciprocal topological superconductors

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 nonreciprocal hopping, which respects particle-hole symmetry (PHS) and dictates that the bulk as well as topological edge modes localize at opposite corners, manifested as the 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 nonreciprocal hopping, where the NHSE is protected by time-reversal symmetry (TRS). The Kramers doublets are localized at opposite corners, namely the TRS protected Z2 NHSE. When an external Zeeman field is applied, its internal symmetry changes from the symplectic class to the orthogonal class, eliminating the NHSE for the states in the spectrum continuum. For the zero-energy states that 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 the 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.

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