报告题目 (Title)：New perspectives on the Bistritzer-MacDonald model and the excitations in twisted bilayer graphene（关于Bistritzer-MacDonald模型和转角双层石墨烯中的激发的新观点）

报告人 (Speaker)：康健 副教授（上海科技大学）

报告时间 (Time)：2022年8月24日(周三) 14:00

报告地点 (Place)：#腾讯会议（147-956-706）

邀请人(Inviter)：张燚

主办部门：理学院物理系

报告摘要：

The Bistritzer-MacDonald (BM) model predicted the existence of the narrow bands in the twisted bilayer graphene (TBG), and nowadays is a starting point for most theoretical works. In this talk, this model with Coulomb interactions will be reviewed from a rather different perspective. We treat this model as an effective field theory defined at atomic energy scale and find that the theory flows toward a fixed point in which the bands are exactly flat [1]. Furthermore, our recent theoretical study reveals the importance of another interlayer tunneling term that was overlooked in all previous works [2,3]. This term non-negligibly breaks the particle-hole symmetry and may have qualitatively changed the properties of the ground state at the charge neutrality point. We further studied the state at the fractional fillings, as well as the associated Landau fan, the electron mass measured by quantum oscillations, and the recently discovered cascade transitions near the integer fillings [4]. Our results not only qualitatively agree with the measurements, but also reveal the emergence of the Fermi liquid at the fractional fillings.

1.Oskar Vafek and Jian Kang, Phys. Rev. Lett, 122, 257602 (2020).

2.Oskar Vafek and Jian Kang, arXiv: 2208.05933.

3.Jian Kang and Oskar Vafek, arXiv: 2208.05953.

4.Jian Kang, B. Andrei Bernevig, and Oskar Vafek, Phys. Rev. Lett, 127, 266402 (2021).