Majorana Edge States in Interacting Two-chain Ladders of Fermions

TL;DR

This paper investigates how strong pair tunneling in interacting two-chain fermion systems leads to Majorana edge states, revealing a topological phase with boundary Majorana modes and ground state degeneracy.

Contribution

It demonstrates the emergence of Majorana edge states in an interacting fermionic ladder model driven by pair tunneling, extending topological superconductor concepts to interacting systems.

Findings

Majorana edge states appear in the strong-coupling phase.

Ground state degeneracy is linked to fermion parity on each chain.

The topological phase is stable against local perturbations.

Abstract

In this work we study interacting spinless fermions on a two-chain ladder with inter-chain pair tunneling while single-particle tunneling is suppressed at low energy. The model embodies a $\mathbb{Z}_2$ symmetry associated with the fermion parity on each chain. We find that when the system is driven to the strong-coupling phase by the pair tunneling, Majorana excitations appear on the boundary. Such Majorana edge states correspond to two-fold degeneracy of ground states distinguished by different fermion parity on each chain, thus representing a generalization of one-dimensional topological superconductors. We also characterize the stability of the ground state degeneracy against local perturbations. Lattice fermion models realizing such effective field theory are discussed.