Theory & Simulation of Twisted Bilayer Materials

近年来，二维材料的扭曲双层膜成为研究强关联电子性质的一个新平台。在这些系统中，两片2D材料以扭曲角堆叠在彼此的顶部，从而产生具有周期性的莫尔图案，其长度尺度可以比底层原子晶格的长度尺度大几个数量级。莫尔图案诱导超晶格势，其降低电子的动能并导致出现在各个层中不存在的相关诱导现象，例如磁性、绝缘行为或甚至非常规超导性。虽然扭曲双层石墨烯是最深入研究的扭曲双层系统，这是由于在以某些“神奇”扭曲角掺杂相关绝缘体状态时的超导性的实验发现，但是存在很大的有前途的扭曲双层系统的空间，其可以通过堆叠其他2D材料（例如过渡金属二硫属化物（TMDC）和六方氮化硼（h-BN））来形成。这些系统的性质在很大程度上仍未被探索。在这个项目中，我们将使用理论和模拟（包括紧束缚和多体方法）来研究候选扭曲双层系统的电子和光学性质，包括TMDC，h-BN和石墨烯，并试图解开这些系统中的超导性。

Recently, twisted bilayers of two-dimensional (2D) materials have emerged as a new platform for studying the properties of strongly-correlated electrons. In these systems, two sheets of 2D materials are stacked on top of each other with a twist angle, resulting in a Moiré pattern with a periodicity that has a length-scale that can be orders of magnitude larger than that of the underlying atomic lattices. The Moire' pattern induces a superlattice potential which reduces the kinetic energy of electrons and results in the emergence of correlation-induced phenomena absent in the individual layers, such as magnetism, insulating behaviour or even unconventional superconductivity. Whilst twisted bilayer graphene is the most intensely studied twisted bilayer system due to the experimental discovery of superconductivity upon doping the correlated insulator state at certain "magic" twist angles, there is a large space of promising twisted bilayer systems that can be formed by stacking other 2D materials such as transition metal dichalcogenides (TMDCs) and hexagonal boron nitride (h-BN). The properties of such systems remain largely unexplored. In this project, we will use theory and simulation (including tight-binding and many-body methods) to investigate the electronic and optical properties of candidate twisted bilayer systems involving TMDCs, h-BN and graphene and attempt to unravel the nature of superconductivity in these systems.