Interaction-driven topological phase transition in correlated symmetry protected topological states

讲座题目：Interaction-driven topological phase transition in correlated symmetry protected topological states

讲座时间：2016年6月14日(周二)下午14:30-16:00

讲座地点：中一楼3113室

报 告 人：孟子扬,中科院物理所特聘研究员(中组部青年千人计划入选者)

报告摘要：

It is expected that the interplay between non-trivial band topology and strong electron correlation will lead to 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 exact Theta=Pi. The bosonic edge states associated with the bosonic SPT states have been directly observed as well. Relevance of these works towards more general interacting symmetry protected topological states will be discussed.

References:

Phys.Rev.B92,165123(2015)

Phys.Rev.B93,115150(2016)

Phys. Rev. B93,195164 (2016)

报告人简介：

从事强关联电子系统的大尺度量子蒙特卡洛模拟研究,探索这些系统中涌现出的新奇量子相变和量子态,取得的学术成绩包括:

(一)运用费米子量子蒙特卡洛方法(1)发现相互作用下的拓扑相变,第一次指出强关联电子系统的拓扑相变不能用单粒子格林函数构造的陈数来描述,而是需要在集体激发中寻找体系的拓扑信息;发现第一个可以用量子蒙特卡洛方法严格计算的bosonic symmetry protected topological (SPT) phase微观模型,为研究具有短程纠缠的拓扑物态及其量子相变铺平了道路。(2 )确定二维Honeycomb晶格Hubbard模型的基态相图,发现强关联格点狄拉克费米子系统中涌现的自旋液体,这是超越Landau-Ginzburg-Wilson相变理论所能描述的新奇量子态的实例;发现强关联格点狄拉克费米子系统从狄拉克半金属到到各种共振价键态(valence bond solid)的量子相变。

(二)运用玻色子量子蒙特卡洛模拟方法(1)确定硬壳玻色子在烧绿石晶格上的基态相图,发现了其中量子自旋冰相,以及量子自旋冰中满足量子电动力学规范场理论描述的低能“光子”激发。为量子自旋冰材料合成,中子、RIXS散射、核磁共振实验探测提供理论指导。(2 )确定三维反铁磁Heisenberg模型从磁有序态到二聚化磁无序态的量子临界行为,验证了上临界维度处的相变对数修正,发现 量子临界点附近的希格斯玻色子振幅模(Higgs mode),为二聚反铁磁体量子临界点附近的中子、RIXS散射实验探测提供理论依据。

发表SCI论文27篇,其中包括Nature一篇,Physical Review Letter 5篇,被引用近900次。

所在单位及职称:中科院物理所,理论室,特聘研究员(中组部青年千人计划入选者)

研究工作经历(按时间倒序排序):

2014/9 –至今,中国科学院物理研究所,理论室,特聘研究员

2013/8 – 2014/8,多伦多大学,博士后,导师:Hae-Young Kee, Yong-Baek Kim

2011/8 – 2013/7,路易斯安那州立大学,博士后,导师:Mark Jarrell