M-valley Moiré Materials in Group IV TMDs

I will present a theory of moiré materials formed from group IV transition metal dichalcogenide (TMD) two-dimensional (2D) semiconductors like HfS₂. I will discuss a set of criteria that must be satisfied in order for the low-energy electronic states in general stacked 2D materials to be accurately described by emergent spatially periodic band Hamiltonians and show that those requirements are satisfied for this class of materials. I will present the resulting model Hamiltonians, which are specified by a small number of parameters, for both homobilayer and heterobilyer materials in this category. The lowest energy conduction bands in group IV TMD moiré materials are spin-degenerate and derive from six degrees of freedom (three orbital × two layer) in three inequivalent M-centered valleys, and their valley projected Hamiltonians are time-reversal invariant. These differences compared to the more studied group VI TMD case give rise to a completely distinct set of competing many-electron states when interactions are included. I will point to some attractive targets for experimental study.