Symmetry and Topology in a Non-Hermitian Kitaev chain

TL;DR

This paper explores the non-Hermitian Kitaev chain, revealing how particle-hole symmetry influences topological phases, Majorana modes, and the skin effect, with a comprehensive phase diagram across complex parameters.

Contribution

It provides a detailed analysis of symmetry, topology, and Majorana modes in a non-Hermitian Kitaev chain, including a new $ ext{Z}_2$ invariant and phase diagram.

Findings

Particle-hole symmetry is preserved across all parameters.

Majorana modes form reciprocal pairs with exact cancellation of skin effect.

A $ ext{Z}_2$ topological invariant distinguishes phases in certain regimes.

Abstract

We investigate the non-Hermitian Kitaev chain with non-reciprocal hopping amplitudes and asymmetric superconducting pairing. We work out the symmetry structure of the model and show that particle-hole symmetry (PHS) is preserved throughout the entire parameter regime. As a consequence of PHS, the topological phase transition point of a finite open chain coincides with that of the periodic (infinite) system. By explicitly constructing the zero-energy wave functions (Majorana modes), we show that Majorana modes necessarily occur as reciprocal localization pairs accumulating on opposite boundaries, whose combined probability density exhibits an exact cancellation of the non-Hermitian skin effect for the zero energy modes. Excited states, by contrast, generically display skin-effect localization, with particle and hole components accumulating at opposite ends of the system. At the level of bulk topology, we further construct a $\mathbb{Z}_2$ topological invariant in restricted parameter regimes that correctly distinguishes the topological and trivial phases. Finally, we present the topological phase diagram of the non-Hermitian Kitaev chain across a broad range of complex parameters and delineate the associated phase boundaries.