激发，自旋电荷分离和关联函数 Excitations, Spin-Charge Separation, and Correlation Function

主讲人：林海青，浙江大学教授，中科院院士

时 间：2023年4月20日10：00-11：30

地 点：物电学院A栋112

联系人：李福祥

讲座摘要：

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 (WR), elegantly characterizes quantum liquid phase diagram. For the TLL phase, WR = 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. Combining quantum integrable theory with numerics, we propose a reliable technique to exactly compute the spectral function of 1D many-body models at large scales and demonstrate the technique on the Lieb-Liniger gas. Our results show that a full description of the critical behavior requires system size as large as thousands of particles.

主讲人简介：

林海青，计算凝聚态物理学专家，美国物理学会会士(2003), 中国科学院院士(2019)。1981年毕业于中国科学技术大学，1983年获得美国爱荷华州立大学理学硕士学位，1987年获得美国加州大学圣地亚哥分校物理学博士学位。北京计算科学研究中心创始人、主任和讲座教授，浙江大学物理学院院长。曾任香港中文大学物理系主任。主要从事凝聚态物性理论和相关的计算物理研究。和合作者一道，预言相分离是强关联系统中的一种普遍现象，并为实验所验证；发现了量子相变与量子纠缠之间的定量关系，从量子信息角度给出以纠缠刻画量子相变新方法；研究了光诱导激发对纳米体系尺寸和空间构型的依赖性，得到的理论结果为实验所验证，并进一步推动了实验工作。