Quasi-Majorana modes in thep-wave Kitaev chains on a square lattice.

Abstract

The topological characteristics of thep-wave Kitaev chains on a square lattice with nearest-neighbor and next-nearest-neighbor inter-chains hopping and pairing are investigated. Besides gapless exact zero-energy modes, this model exhibits topological gapless phase hosting edge modes, which do not reside strictly at zero energy. However, these modes can be distinguished from the bulk states. These states are known as pseudo- or quasi-Majorana Modes (qMMs). The exploration of this system's bulk spectrum and Berry curvature reveals singularities and flux-carrying vortices within its Brillouin zone. These vortices indicate the presence of four-fold Dirac points arising from two-fold degenerate bands. Examining the Hamiltonian under a cylindrical geometry uncovers the edge properties, demonstrating the existence of topological edge modes. These modes are a direct topological consequence of the Dirac semimetal characteristics of the system. The system is analyzed under open boundary conditions to distinguish the multiple Majorana zero modes and qMMs. This analysis includes a study of the normalized site-dependent local density of states, which pinpoints the presence of localized edge states. Additionally, numerical evidence confirms the topological protection of the edge states due to the finite-size effect and their robustness against disorder perturbations. The emergence of topological edge states and Dirac points with net zero topological charge indicates that this model is a weak topological superconductor.