Session 2-2

Abstract

Recently, moiré materials, which are artificially stacked 2D systems with slight mismatches between layers, attract much attentions. The slight mismathes induces long range moiré pattrens, and can have striking effects on electronic band structures. An example is a twisted bilayer system where the moiré length scale is controlled by its twist angle. A typical consequece of a long range moire pattern is emergence of flat electronic bands that enhance electron-electron correlation effects as in twisted bilayer graphene [1].
In this study, a honeycomb monolayer material BC₃, which can be regarded as regularly B-doped graphene, is found to show interesting properties after making twisted bilayers [2]. The previous theoretical study suggests that monolayer BC₃ is a semiconductor with three valleys. The first-principles density functional theory is used to derive a low-energy effective model and fix necessary parameters to obtain band structures in twisted bilayer setups. The analysis of the obtained model shows that the originally 2D band dispersions are squeezed into quasi-1D ones upon making twisted bilayers. Interestingly, the quasi-1D directionality depends on the valley, indicative of valley dependent transport and potential uses for valleytronics applications. Also, the valley dependence reduces to valley dependent spin-spin interactions in a strongly correlated limit, which may lead to exotic quantum phases where spin and valley degrees of freedom are intertwined.