Prof. Zi Yang Meng (Institute of Physics, Chinese Academy of Sciences)
"Interaction-driven topological phase transition in correlated SPT states"
It is expected that the interplay between non-trivial band topology and strong electron correlation will lead to very rich physics.
Thus a controlled study of the competition between topology and correlation is of great interest. Here, employing large-scale quantum
Monte Carlo simulations, I will introduce a concrete example of the Kane-Mele-Hubbard model on an AA stacking bilayer honeycomb lattice
with inter-layer antiferromagnetic interaction. Our simulations identified three different phases: a quantum spin-Hall insulator (QSH),
a xy-plane antiferromagnetic Mott insulator and an inter-layer dimer-singlet insulator. Most importantly, an exotic topological phase
transition between the QSH and the dimer-singlet insulators, purely driven by the inter-layer antiferromagnetic interaction is found.
At the transition, the spin and charge gap of the system close while the single-particle excitations remain gapped, which means that
this transition has no mean field analogue and can be viewed as a transition between bosonic SPT states. This transition is described
by a (2+1)d O(4) nonlinear sigma model with exact SO(4) symmetry, and a topological term at exactly Theta=Pi. I will also discuss a new,
general technique -- strange correlator -- that we have developed to directly minitor the edge states of topological insulators in the
presence of interaction. Relevance of these works towards more general interacting SPT states is discussed.
References:
http://arxiv.org/abs/1506.00549
http://arxiv.org/abs/1508.06389