Title: Excitations, Spin-Charge Separation, and Quantum Phase Transition

Hai-Qing Lin

Beijing Computational Science Research Center

Abstract:

Quasi-particles play important role in condensed matter physics and result in many emergent novel phenomena. In this talk, we discuss collective excitations in one-dimension as exemplified by antiferromagnetic Heisenberg model and δ-function interacting Fermi gas (Yang-Gaudin model). Using the thermodynamic Bethe ansatz (TBA) formalism, we analytically derive universal properties of the models with arbitrary interaction strength, and present a rigorous understanding of spin-charge separation, a unique feature predicted by the Tomonaga-Luttinger liquid (TLL) theory.  Spinon, as an elementary spin excitation, is responsible for the TLL. We show that a dimensionless quantity, the Wilson ratio (RW), elegantly characterizes quantum liquid phase diagram. For the TLL phase, RW = 4Ks remains almost temperature independent, where Ks is the Luttinger parameter. WR can be used to identify quantum phase transitions for a wide variety of materials. Based on the exact low-lying excitation spectra, we further evaluate the spin and charge dynamical structure factors (DSFs). The peaks of the DSFs exhibit distinguishable propagating velocities of spin and charge as functions of interaction strength, which can be observed by Bragg spectroscopy with ultracold atoms.

Acknowledgements: NSAF U1930402 and NSFC 11734002, as well as computational resources from the Beijing Computational Science Research Center

Collaborators:

Guan XW Group: Feng He, Yu-Zhu Jiang, Yi-Cong Yu, Yang-Yang Chen,

Rich Univ./US: Randall G. Hulet, Han Pu

Univ. of Warwick/UK: Rudolf A. Romer

Bethe Ansatz Group: X.-G. Yin A. Foerster, M. T. Batchelor, C.-H. Lee

简历

林海青, 教授。

1981年在中国科学技术大学获得学士学位。1980年参加CUSPEA项目。

1983年在美国Iowa州立大学获得理学硕士学位。

1987年在美国加州大学San Diego分校物理系获得物理学博士学位。

1987年至1989年在美国Brookhaven国家实验室任副研究员（Research Associate）。

1989年至1991年在美国Los Alamos国家实验室任副研究员（Research Associate）。

1991年10月至1995年7月在美国University of Illinois at Urbana-Champaign物理系任Research Assistant Professor。

1995年8月至2012年9月在香港中文大学物理系任副教授、教授。

2009年8月至今任中国工程物理研究院、北京计算科学研究教授。

主要从事凝聚态物理和计算物理的研究。

主要研究兴趣包括：

强关联系统，量子纠缠和量子相变，以及多体系统的数值方法。