应6163银河net163am赵继泽副教授邀请，中国人民大学刘正鑫副教授来我院访问，并做学术报告。欢迎广大师生届时参加！

题目：Field induce spin liquids in honeycomb lattice K-Γ model and the relation to α-RuCl3

时间：2018年7月27日下午3:00

地点：格致楼4022

报告摘要：

Using Variational Monte Carlo computation, we study the $K$-$Gamma$ model on the honeycomb lattice. Besides the Kitaev spin liquid (SL) phase, a gapless $Z_2$ SL and two field-induced quantum SL phases are found. It is shown that the gapless Kitaev SL phase undergoes a first order phase transition to a zigzag ordered state with the increasing of $Gamma/|K|$. At a small intermediate region, we find a gapless $Z_2$ SL phase which is different from the ground state of the pure Kitaev model. When $Gamma/|K|$ increases further, the system enters the zigzag ordered phase again. This gapless SL phase survives if a small nearest-neighbor Heisenberg interaction is considered. By fixing $Gamma/|K|=1.4$ (fitted from spin-wave spectrum of $alpha$-RuCl$_3$ in neutron scattering) and adding a magnetic field, we observe a phase transition from zigzag magnetic ordered phase to a partially polarized disordered phase. The nature of this state depends crucially on the field orientation. For particular field directions in the honeycomb plane, a gapless Dirac SL is induced, in agreement with recent Nuclear Magnetic Resonace experiments on $alpha$-RuCl$_3$. For a range of out-of-plane fields, we find a Kalmeyer-Laughlin-type chiral SL, which would show a quantized thermal Hall effect.

报告人简介：

刘正鑫于2010年在香港科技大学获得博士学位，同年作为C.N. Yang Junior fellow博士后在清华大学高等研究院工作。2012至2015年作为继续留在清华大学高等研究院任副研究员。曾多次到麻省理工学院、加拿大理论物理圆周研究所等访问。2015年至今为中国人民大学物理系副教授。刘正鑫博士的研究领域主要包括强关联系统中的拓扑序对称保护拓扑序和阻挫量子磁性系统。