Speaker
Cenke Xu
Description
We discuss our recent works on strongly interacting bilayer
quantum Spin Hall insulators with Sz conservation. We
demonstrate that interaction will drive the system into a
"bosonic" symmetry protected topological phase, in the sense
that bosonic modes are gapless at the boundary, while local
fermion excitations are gapped. Also, at the bulk quantum
critical point between the topological and trivial states,
bosonic modes close their gap, while fermion modes remain
gapped. Thus this quantum critical point is a purely "bosonic"
conformal field theory, which is described by a 2+1d O(4)
nonlinear sigma model with a Theta term at Theta = Pi. All
these results are confirmed by both field theory analysis and
also quantum Monte Carlo simulation. We also propose that
these physics can be well realized in bilayer graphene under
(strong) out of plane magnetic field.
