Evolution of the T-Pfaffian surface state at the topological-insulator critical point

Determine how a gapped T-Pfaffian topologically ordered surface state evolves as a three-dimensional time-reversal-invariant topological insulator approaches the transition to a trivial insulator.

Background

The paper analyzes boundary criticality at the transition between a (3+1)-dimensional time-reversal-invariant topological insulator and a trivial insulator using a Dirac mass domain wall. In the noninteracting setting, the critical boundary fermion acquires the scaling dimension of the bulk Dirac fermion, while the gapped topological-insulator phase supports a surface Dirac cone.

Interactions permit an alternative gapped, topologically ordered surface termination known as the T-Pfaffian state. The paper does not analyze this interacting boundary state or its behavior as the bulk gap closes, leaving unresolved whether and how its topological order, excitations, and boundary critical properties evolve at the topological-insulator transition.