Condensed Matter Physics Seminar

The surfaces of three dimensional topological insulators (3D TI) are generally described as Dirac metals, with a single Dirac cone. It was previously believed that a gapped surface implied breaking of either time reversal or charge conservation symmetry. Here we discuss a novel possibility in the presence of interactions, a surface phase that preserves all the symmetries but is nevertheless gapped and insulating. The surface develops a topological order similar to the nonabelian quantum Hall (Moore-Read) Pfaffian state. When realized in 2D, it has a Hall conductance of 1/2 and hence explicitly breaks time reversal symmetry. However, by constructing exactly solvable models, we show that it can appear as the time reversal symmetric surface state of 3D TI.