In this work, we study interacting spinless fermions on a two-chain ladder with interchain 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 an effective field theory are discussed.

• Received 15 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.094503