报告题目：Bond bipolarons and high-temperature superconductivity

报 告 人：张超  访问学者 （中国科学技术大学）

邀 请 人：张进

时  间：2023年5月8号（星期一）上午10:00

地   点：bat365官网登录入口LE523

Abstract: It has been assumed for decades that high values of T_c from the electron-phonon coupling are impossible. At weak-to-intermediate coupling strength, this result follows from the Migdal-Eliashberg theory, while at strong coupling, when bipolarons form, the transition temperatures are low because of the large effective mass enhancement. However, the latter conclusion was based on numerical solutions of the Holstein model. Here I present a different model with electron-coupling based on the displacement modulated hopping of electrons (bond Su-Schrieffer-Heeger model) and argue that much larger values of the bipolaron T_c can be achieved in this setup. We use an exact sign-problem-free quantum Monte Carlo approach to study the property of both Holstein and bond bipolarons with and without short- and long-range Coulomb interactions. The T_c in the bond bipolaron model generically and significantly exceeds typical upper bounds based on Migdal-Eliashberg theory or superfluidity of Holstein bipolarons. The key ingredient in this bipolaronic mechanism that gives rise to high T_c is the combination of light mass and small size of bipolarons. Our work establishes principles towards the design of high-T_c superconductors via functional material engineering.

Ref: PRX 13(1), 011010(2023); PRB 105, L020501(2022); arXiv:2210.14263.

Brief CV: 张超，2018年12月获得美国俄克拉荷马大学物理学博士学位，后在德国萨尔大学，美国马萨诸塞大学阿默斯特分校从事博士后研究员工作。2021.06-2023.02为华东师范大学精密光谱科学与技术国家重点实验室副研究员。现为中国科学技术大学访问学者。长期从事基于蒙特卡洛方法对强相互作用多粒子体系的研究，在 Physical Review X, Physical Review B, Physical Review A 和 New Journal of Physics 等国际知名期刊发表论文18篇，一作14篇。