A coupled wire model of a symmetry-preserving massive surface state of a fractional topological insulator

The surface Dirac fermion of a topological insulator cannot turn massive in the single-body setting without breaking charge conservation or time-reversal symmetry. Under many-body interactions, the surface state can acquire an excitation energy gap while preserving the symmetries and support fractional anyonic surface excitations. Example includes the T-Pfaffian and Pfaffian-antisemion surface topological order. The built-in many-body interacting nature of a fractional topological insulator (FTI) -- a topological insulator of fractionally charged partons -- renders the generalization of the single-body Dirac surface state somewhat irrelevant. In fact, it was shown in our previous analysis that a symmertry-preserving massive surface state exists. Here, using an exactly-solvable coupled wire model, we construct an explicit microscopic theory of the fractional surface state and discuss a particle-vortex duality.