郭硕鸿讲座（第六十一期）2024年3月29日16:40：Fully frustrated XY spin model on a Kagome lattice with a 1/3 fractional vortex-antivortex pairing phase transition

 主持人：姚道新教授

报告简介：A general framework has been developed to solve the two-dimensional fully frustrated XY spin model on a Kagome lattice. The essential idea is to encode the ground-state local rules induced by frustrations in the local tensors of the partition function. Then the partition function is expressed in terms of a product of one-dimensional transfer matrix operator, whose eigen-equation can be solved by an algorithm of variational uniform matrix product states rigorously. The singularity of the entanglement entropy for the one-dimensional quantum analogue provides a stringent criterion to distinguish various phase transitions without identifying any order parameter a prior. Specially, we introduced a new representation to build the tensor network with local tensors lying on the centers of the elementary triangles of the Kagome lattice based on the duality transformation. Through a systematic numerical analysis of thermodynamic properties and correlation functions in the thermodynamic limit, we numerically proved that the model exhibits a single Berezinskii-Kosterlitz-Thouless phase transition, which is driven by the unbinding of 1/3 fractional vortex-antivortex pairs. Our result may be used to understand the charge-6e condensate observed experimentally in the vortex-antivortex lattice phase of the Kagome superconductors.

1. Tensor network approach to the fully frustrated XY model on a kagome lattice with a fractional vortex-antivortex pairing transition,

Feng-Feng Song and Guang-Ming Zhang, Phys. Rev. B 108, 014424 (2023).

1. Evidence for multi-charge flux quantization in kagome superconductor ring devices,

Jun Ge, Pinyuan Wang,Ying Xing, Qiangwei Yin, Anqi Wang, Jie Shen, Hechang Lei, Ziqiang Wang & Jian Wang, arXiv:2201.10352v2.

报告人简介：张广铭教授，1991年获上海交通大学凝聚态物理学博士学位，先后在意大利国际理论物理中心（ICTP）和伦敦帝国理工大学任研究助理。1997年，任清华大学高等研究中心研究员，2004年至今, 任清华大学物理系教授，现任清华大学凝聚态物理研究所所长和低维量子物理国家重点实验室副主任。长期研究凝聚态物理学中的量子多体问题，提出严格求解二维Kitaev量子自旋模型的新方法；建立二维量子数分数化激发的统一理论；构建一维量子整数自旋链拓扑态的普适类；发展关联电子多体系统中近藤共振和磁性关联的量子多体理论。1999年获香港求是科技基金会“杰出青年学者”奖，2001年获“国家杰出青年基金”资助，2006年入选国家重大人才计划工程项目，2011年获中国物理学会“叶企孙物理奖”。