学术报告（12月17日）

主持人：姚道新教授

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摘要： 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 renders this transition no mean field analogue and 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 symmetry protected topological states will be discussed.

 
References:
1. Phys. Rev. B 92, 165123 (2015)
2. http://arxiv.org/abs/1508.06389
3. http://arxiv.org/abs/1510.07816

报告人简介： 孟子杨，青年海外高层次人才，中科院物理所百人计划，副研究员。他于中国科技大学获得本科学位，德国斯图加特大学获得博士学位，之后在美国路易斯安那州立大学做Postdoc。长期从事强关联电子系统，特别是量子蒙特卡罗、动力学平均场（DMFT）等的研究。