CMT Seminar today at 11:30 am

[Palmer, Shelley]

Please take note of CMT seminar taking place today -  Monday, March 21, 2016 at 11.30 AM in The Robert Smith Seminar Room. Details concerning the talk are as follows:

Speaker:         Cenke Xu (University of California, Santa Barbara)
Date:               Monday, March 21, 2016
Time:               11.30 AM
Place:              1080 Physics Research Building, The Robert Smith Seminar Room
Title:                Experimental Platform for Bosonic Symmetry Protected Topological States


Abstract: Bosonic symmetry protected topological (BSPT) states, i.e. bosonic analogue of topological insulators, have attracted enormous theoretical interests and efforts in the last few years. Although the BSPT states have been successfully classified with various approaches, there has been no successful experimental realization of BSPT states yet in two and higher dimensions. In this paper, we propose that the two dimensional BSPT state with U(1)×U(1) symmetry can be realized in a bilayer graphene under an out-of-plane magnetic field, where the two U(1) symmetries stand for the total spin and total charge conservation respectively. The Coulomb interaction plays a central role in this proposal: (1) it gaps out all the fermions at the boundary of the system, hence the remaining symmetry protected gapless boundary states only have bosonic charge and spin degrees of freedom; (2) based on the conclusion above, we propose that the bulk quantum phase transition between the BSPT and trivial phase, which can be driven by a competition between the out-of-plane magnetic field and electric field, under strong interaction can become a "bosonic phase transition", i.e. only bosonic modes close their gap at the transition. This transition is fundamentally different from all the well-known topological-trivial transition in the free fermion topological insulators. The latter statement is supported by recent determinant quantum Monte carlo simulation on a similar sign-problem-free model on a bilayer honeycomb lattice.


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