Fermionic Matrix Product States and One-Dimensional Topological Phases

TL;DR

This paper introduces fermionic matrix product states (fMPS), classifies their types, and explores their role in understanding topological phases and symmetry-protected states in one-dimensional fermionic systems.

Contribution

The work formalizes fMPS, classifies their irreducible forms, and connects them to topological invariants and symmetry classifications in interacting fermionic phases.

Findings

fMPS fall into two classes related to $ ext{Z}_2$ graded algebras

Majorana edge modes cause two-fold degeneracy in entanglement spectrum

fMPS formalism links $ ext{Z}_8$ classification to Clifford algebra representations

Abstract

We develop the formalism of fermionic matrix product states (fMPS) and show how irreducible fMPS fall in two different classes, related to the different types of simple $\mathbb{Z}_2$ graded algebras, which are physically distinguished by the absence or presence of Majorana edge modes. The local structure of fMPS with Majorana edge modes also implies that there is always a two-fold degeneracy in the entanglement spectrum. Using the fMPS formalism we make explicit the correspondence between the $\mathbb{Z}_8$ classification of time-reversal invariant spinless superconductors and the modulo 8 periodicity in the representation theory of real Clifford algebras. Studying fMPS with general on-site unitary and anti-unitary symmetries allows us to define invariants that label symmetry-protected phases of interacting fermions. The behavior of these invariants under stacking of fMPS is derived, which reveals the group structure of such interacting phases.We also consider spatial symmetries and show how the invariant phase factor in the partition function of reflection symmetric phases on an unorientable manifold appears in the fMPS framework.