Quantum Matter Seminar: Electrical Breakdown of Excitonic Insulators

戴希

香港科技大学

报告时间：2024年10月8日（周二）下午15:30

报告地点：紫金港校区段永平教学楼2号楼212报告厅

摘要：

In this paper, we propose a new electrical breakdown mechanism for exciton insulators in the BCS limit, which differs fundamentally from the Zener breakdown mechanism observed in traditional band insulators. Our new mechanism results from the instability of the many-body ground state for exciton condensation, caused by the strong competition between the polarization and condensation energies in the presence of an electric field. We refer to this mechanism as “many-body breakdown”. To investigate this new mechanism, we propose a BCS-type trial wave function under finite electric fields and use it to study the many-body breakdown numerically. Our results reveal two different types of electric breakdown behavior. If the system size is larger than a critical value, the Zener tunnelling process is first turned on when an electrical field is applied, but the excitonic gap remains until the field strength reaches the critical value of the many-body breakdown, after which the excitonic gap disappears and the system becomes a highly conductive metallic state. However, if the system size is much smaller than the critical value, the intermediate tunnelling phase disappears since the many-body breakdown happens before the onset of Zener tunnelling. The sudden disappearance of the local gap leads to an “off-on” feature in the current-voltage (I − V ) curve, providing a straightforward way to distinguish excitonic insulators from normal insulators.

报告人简介：

戴希，理论物理学家，香港科技大学物理学系讲座教授。1999年博士毕业于中国科学院理论物理研究所，曾先后在香港科技大学、美国波士顿学院和新泽西州立罗格斯大学从事博士后研究；2004年进入香港大学物理系工作；2007年回到中国科学院物理研究所工作，担任研究员、博士生导师；2009年担任北京凝聚态物理国家实验室副主任；2011年获得国家杰出青年科学基金资助；2017年进入香港科技大学工作；2023年获第二期新基石研究员项目资助。戴希教授一直从事强关联电子材料、计算材料科学、量子磁学、超导体和非常规超导体方面的研究，迄今共发表SCI论文200余篇，被引5万余次，2014年起连续十年入选科睿唯安“全球高被引科学家”，曾获中国科学院青年科学家奖，全球华人物理学会亚洲杰出科技成就奖，周光召基础科学奖，周培源物理奖，美国物理学会会士，美国物理学会James C. McGroddy 新材料奖等。