激發，自旋電荷分離和關聯函數 Excitations, Spin-Charge Separation, and Correlation Function
主講人：林海青，浙江大學教授，中科院院士
時 間：2023年4月20日10：00-11：30
地 點：物電學院A棟112
聯系人：李福祥
講座摘要：
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.
主講人簡介：
林海青，計算凝聚態物理學專家，美國物理學會會士(2003), 中國科學院院士(2019)。1981年畢業于中國科學技術大學，1983年獲得美國愛荷華州立大學理學碩士學位，1987年獲得美國加州大學圣地亞哥分校物理學博士學位。北京計算科學研究中心創始人、主任和講座教授，浙江大學物理學院院長。曾任香港中文大學物理系主任。主要從事凝聚態物性理論和相關的計算物理研究。和合作者一道，預言相分離是強關聯系統中的一種普遍現象，并為實驗所驗證；發現了量子相變與量子糾纏之間的定量關系，從量子信息角度給出以糾纏刻畫量子相變新方法；研究了光誘導激發對納米體系尺寸和空間構型的依賴性，得到的理論結果為實驗所驗證，并進一步推動了實驗工作。
