郭硕鸿讲座（第三十四期）（2023年4月20日15：00）：The emergence and disappearance of high Tc superconductivity

主持人：王雪华 教授

报告简介：The mechanism of high temperature superconductivity in the copper oxides (cuprates) remains an outstanding puzzle despite more than 30 years of intense research. One of the few consensuses is that the parent compound is a Mott insulator with strong onsite Coulomb repulsion, and superconductivity emerges when the doped charge carriers become mobile. However, when too many holes are introduced into the system, superconductivity disappears and it becomes a metal. A key task in unveiling the mystery of superconductivity in cuprate is to understand the electronic structure evolution from the doped Mott insulator perspective.

In this talk, we report scanning tunneling microscopy studies of the atomic scale electronic structure of cuprates with increasing doping levels. We first show the observation of charge transfer gap in the parent Mott insulator, and its anticorrelation with the maximum transition temperature. It implies that the superexchange interaction plays a central in mediating the Cooper pairing. We then show how the low energy electronic states emerge within the charge transfer gap when few holes are introduced into the parent Mott insulator. They can be regarded as hydrogen atom and molecule in a Mott insulator background, and exhibit characteristic spatial distributions. When a few percent of holes are dispersed into the Mott insulator, they self-assemble into small islands of checkerboard consisting of puddles with size around 4a0. Even in the insulating sample, we observe a small superconducting-like gap when approaching the checkerboard island from the Mott insulator phase. Across the insulator to superconductor transition, the local spectra remain qualitatively similar, and the main difference is the enhancement of quasiparticle interferences characteristic of long-range phase coherence. We find that each checkerboard puddle contains approximately two holes, and exhibit stripy internal patterns that have strong influence on the superconducting properties. With further increase of doping into the overdoped regime, the strong quasiparticle scattering in the antinodal region causes pair breaking, which is the driving force for the vanishing of superconductivity. These results shed important new lights on the emergence and disappearance of superconductivity in cuprates high Tc superconductors.

报告人简介：王亚愚， 1998年本科毕业于中国科技大学物理系，2004年在美国普林斯顿大学物理系获得博士学位，2004年至2007年在美国加州大学伯克利分校物理系任Miller Research Fellow。2007年12月加入清华大学物理系任教授，曾任低维量子物理国家重点实验室主任、清华大学物理系主任、理学院院长，现任清华大学学科规划与建设办公室主任。

研究领域为凝聚态物理实验，近期的主要研究方向为拓扑量子材料的低温强磁场输运性质和高温超导体的扫描隧道显微学研究。他在量子反常霍尔效应的实验发现、强关联与拓扑电子体系的量子输运现象、高温超导体的微观电子结构等领域取得多项研究成果。曾获得2006年William McMillan Award 、2006年教育部“长江学者”特聘教授、2008年美国李氏基金会“杰出成就奖”、2009年国家自然科学基金委杰出青年基金、2013年中国科协“青年科技奖”、2013年低温物理学会“马丁-伍德爵士中国奖”、2015年中国物理学会“黄昆物理奖”、2016年万人计划创新领军人才、2018年国家自然科学一等奖（第二完成人）、2019年腾讯“科学探索奖”、2023年入选首批“新基石研究员”计划。