Fractional statistics of topological defects in graphene and related structures

We show that fractional charges bound to topological defects in the recently proposed time-reversal-invariant models on honeycomb and square lattices obey fractional statistics. The effective low-energy description is given in terms of a doubled'' level-2 Chern-Simons field theory, which is parity and time-reversal invariant and implies two species of semions (particles with statistical angle +/- pi/2) labeled by a new emergent quantum number that we identify as the fermion axial charge.