Quantum Phase Transition between Integer Quantum Hall States of Bosons
  Bosonic Integer Quantum Hall (IQH) phases are a class of symmetry protected topological (SPT) phases that, similar to the fermionic IQH states, support a quantized Hall conductance. They, however, require interactions for their realization. Here we study quantum Hall plateau transitions between a trivial insulator and a bosonic IQH phase, in a clean system. Generically, we find an intervening superfluid phase. The presence of additional symmetries, however, can potentially lead to a direct transition between these phases. We employ a fermionic parton description that captures both the insulating phases as well as the transition between them. The critical theory is massless QED-3 with Nf = 2 fermion flavors. The fermions have a surprisingly simple interpretation - they are vortices of the superfluid. Therefore the universal conductivity at the transition, assuming it is continuous, equals the universal resistivity of Dirac fermions in QED-3. We also briefly comment on sigma model descriptions of the transition and the surface states of related 3D SPT phases. 
Tarun Grover and Ashvin Vishwanath
cond-mat.str-el cond-mat.mes-hall hep-th