Topic: Topological moiré trilayers
Speaker: Professor Mikito Koshino, Department of Physics, Osaka University (Osaka-U)
Date and time: April 30, 14:30–16:00
Venue: Zoom Meeting
Meeting ID: 279 922 5081 Password: 20201203
Host: Liu Jianpeng
Abstract:
In addition to the extensive study of twisted moiré bilayers in the past decade, the scope of investigation has extended to encompass multilayer systems including three or more layers. Particular attention has recently been directed toward twisted trilayer systems, which consist of three layers arranged in a specific rotational configuration. A twisted trilayer is characterized by two twist angles between adjacent layers, offering a vast parameter space that remains largely unexplored. In the first part of my talk, we will present systematic theoretical studies on the lattice relaxation and the electronic structures in general twisted trilayer graphenes. We show that the relaxed lattice structure forms a patchwork of moiré-of-moiré domains, where two moiré patterns become locally commensurate. The electronic band calculation reveals a wide energy window featuring highly one-dimensional electron bands, which are identified as a topological boundary state between distinct Chern insulators. In the latter part, we will explore the electronic structure of hBN/graphene/hBN trilayer system with arbitrary twist angles. We find that the electronic spectrum displays fractal minigaps akin to the Hofstadter butterfly. Each of minigaps is uniquely labeled by six topological numbers associated with the quasicrystalline Brillouin zones, and these numbers can be expressed as second Chern numbers through a formal connection with the quantum Hall effect in four-dimensional space.
Biography:
Dr. Koshino received his PhD degree from University of Tokyo in 2003. He was a research associate in Tokyo Institute of Technology from 2003 to 2010, and he was an associate professor in Tohoku University from 2010 to 2016. Since 2016, he has taught in Osaka University, where he is a professor in the Department of Physics. His current research focuses on the theoretical study on the electronic properties of 2D materials and also covers the topological materials.