【报告题目】：Strong correlations meet electron-phonon coupling
【报告人】：王强华教授，南京大学
【报告时间】：12月6日（周五）9：00
【报告地点】：科技楼29-414
【报告摘要】：In this talk, I discuss several remarkable effects when strong electron correlations coexist with electron-phonon coupling. [1] In high-Tc cuprates, the isotope exponent diminishes around optimum doping, but the exponent diverges positively in underdoped and overdoped regimes. We propose a two-boson model, with one of the modes being phonons, and find that the experimental anomalous isotope effect can be nicely explained if both of the boson modes are attractive for d-wave pairing. [2] We substantiate the phenomenological model in [1] by functional renormalization group calculations in a microscopic Hubbard model with Hubbard interaction and various types of optical phonon modes. We find all Holstein-like phonons suppress the d-wave SC, leading to negative isotope effect, while the SSH-type phonons enhance d-wave SC, leading to positive isotope exponent that diverges where Tc itself vanishes, in nice agreement with experiments. [3] We also discuss the effect of strong electron-phonon coupling coexisting with strong electron correlations. We find a rich variety of competing orders in square lattices and Kagome lattices, with either positive or negative isotope effects, shedding lights on possible avenue in achieving higher superconducting transition temperature by utilizing electron-phonon coupling in correlated materials. Wherever applicable, the results are confirmed by quantum Monte Carlo.
References:
[1] Sun G, Luo PX, Lai SQ, Wang, D and Wang QH, New J Phys 23, 053006 (2021).
[2] Wang D, Wang WS and Wang QH, Phys Rev B 92, 195102 (2015).
[3] Yang QG, Wang D, and Wang QH, Phys Rev B 106, 245136L (2022).
[4] Yang QG, Yao M, Wang D, and Wang QH, Phys Rev B 109, 075130 (2024)
[5] Sun G, Yang QG, Wang D and Wang QH, Phys Rev B 109, L180508 (2024)
【报告人简介】：王强华教授，1993年于南京大学获博士学位，之后留校工作。1995-1997年在香港大学做博士后研究工作，2000-2002年在加州伯克利大学访问研究，2002年起任南京大学教授。获2003年度国家杰出青年基金资助，受聘2006-2009年度教育部长江学者特聘教授。获国家教委科技进步奖1项，江苏省科学技术奖1项。从事凝聚态理论方面的研究，主要研究方向为强关联电子系统中的超导等物质态的物理性质及其微观机理。发表Nature, Phys. Rev. Lett, Phys. Rev. X, Nature Physics, Nature Communications, Phys. Rev. B等论文多篇。提出并命名准粒子散射相干效应；提出和发展处理强关联系统物理的非约束及有限温情况下的重整化平均场方法；提出和发展基于费米子双线性散射模式分解的泛函重整化群方案; 揭示和发现若干强关联体系中的超导微观机理和超导配对特性，以及其它相关磁性和拓扑物质态特性。
