柏林自由大学

Isolated Bloch bands with nearly flat dispersion are natural playgrouds of interacting many-body states of electrons. Recent years, highly tunable flat band structures appear in 2D moiré materials. Experiments have observed rich phase diagrams of correlated electrons, including those states with intrinsic topological orders, the fractional Chern insulators. These states are particularly interesting due to their potential to host fractional statistics in the absence of a strong magetic field. These phenemena drive surging demand in undertanding the origin of the correlated states and their competitions. In this presentation, I will show how geometry of quantum states provides an intuivie picture of partially filled flat bands, and sometimes reduces the strongly interacting question to a weakly interacting question. I will start from showing that the phase part of the quantum geometry, Berry curvature, does not play a decisive role as expected empirically. In contrast, the other component of quantum state geometry, the quantum distance and its leading-order expansion, the Fubini-Study metric, dictate where electrons tend to occupy in the Brillouin zone. This leads to an emergent particle-hole asymmetry and a guideline of the many-body phase diagram. I will give examples for the application of this picture in severel twisted muti-layer graphene systems.

报告人简介：

杨康，本科毕业自北京大学，于巴黎高等师范学院和巴黎索邦大学取得硕士和博士学位。曾在斯德哥尔摩大学Emil Bergholz组作博士后，现为柏林自由大学Felix von Oppen组博士后。研究方向包括陈绝缘体，含时驱动体系和耗散光子能带系统。

地点：M楼830

邀请人：杨义峰，18911600270，yifeng@iphy.ac.cn