Twisted 2D systems: playgrounds for strongly-correlated phenomena
Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
In this talk, I will talk about our recent developments on studying the electronic properties and correlation effects in twisted bilayer systems, which are inspired by the recent experimental breakthrough on twisted bilayer graphene (TBG). It was suggested that twisted bilayer graphene near the so called "magic angles" could be an ideal platform for the study of strongly correlated physics and unconventional superconductivity. Our studies show that some other twisted bilayer systems could also be used to study those exotic correlated effects without the constrains set by magic angles and with even richer physics. In particular, with first principle methods, we show that flat bands also develop at the band edges of twisted bilayer Boron nitride (TBBN). Moreover, instead of one pair of flat bands as in TBG, multiple flat bands appear in TBBN with different characters, which can potentially give rise to richer correlated phenomena and also Moire exciton physics. In another twisted 2D system with rectangular symmetry, namely, twisted bilayer GeSe, we show that the low-energy states can be turned into an effective 1D system with a narrow bandwidth. This not only allows us to study the necessarily collective nature of excitations in one dimension, but can also serve as a promising platform to scrutinize the crossover from two to one dimension in a controlled setup by varying the twist angle, which provides a novel benchmark to theory. We thus establish twisted bilayer GeSe as an intriguing inroad into the strongly correlated physics of low-dimensional systems.
Brief CV of Dr. Lede Xian:
Dr. Xian obtained his Ph.D . in 2014 from Georgia Institute of Technology in the USA under the supervision of Prof. Mei-Yin Chou. He is currently a postdoc researcher at the Max Planck Institute for the Structure and Dynamics of Matter working with Prof. Angel Rubio. Dr. Xian is a theoretical physicist with extensive experience in density functional theory calculations and novel 2D materials research. He has contributed to the exploration of novel elemental 2D materials, ultra-fast band gap renormalization of VO2 and plasmonic properties of 2D heterostructures. His recent interest lies in the study of twisted 2D systems.