激發(fā)，自旋電荷分離和關(guān)聯(lián)函數(shù) Excitations, Spin-Charge Separation, and Correlation Function

主講人：林海青，浙江大學(xué)教授，中科院院士

時(shí) 間：2023年4月20日10：00-11：30

地 點(diǎn)：物電學(xué)院A棟112

聯(lián)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(jiǎn)介：

林海青，計(jì)算凝聚態(tài)物理學(xué)專家，美國(guó)物理學(xué)會(huì)會(huì)士(2003), 中國(guó)科學(xué)院院士(2019)。1981年畢業(yè)于中國(guó)科學(xué)技術(shù)大學(xué)，1983年獲得美國(guó)愛(ài)荷華州立大學(xué)理學(xué)碩士學(xué)位，1987年獲得美國(guó)加州大學(xué)圣地亞哥分校物理學(xué)博士學(xué)位。北京計(jì)算科學(xué)研究中心創(chuàng)始人、主任和講座教授，浙江大學(xué)物理學(xué)院院長(zhǎng)。曾任香港中文大學(xué)物理系主任。主要從事凝聚態(tài)物性理論和相關(guān)的計(jì)算物理研究。和合作者一道，預(yù)言相分離是強(qiáng)關(guān)聯(lián)系統(tǒng)中的一種普遍現(xiàn)象，并為實(shí)驗(yàn)所驗(yàn)證；發(fā)現(xiàn)了量子相變與量子糾纏之間的定量關(guān)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(dǎo)激發(fā)對(duì)納米體系尺寸和空間構(gòu)型的依賴性，得到的理論結(jié)果為實(shí)驗(yàn)所驗(yàn)證，并進(jìn)一步推動(dòng)了實(shí)驗(yàn)工作。