Two-dimensional valley-layer coupling heterostructures

Coupling valleys with different layers is a feasible way to realize valley polarization through a gate electric field, but only a few two-dimensional (2D) materials with locked valley and layer physics have been found so far. In this Letter, we show that valley-layer coupling (VLC), which is robust against spin–orbit coupling, could be achieved in 2D heterostructures built using distinct 2D monolayers with no VLC feature, as demonstrated by density functional theory calculations on Tl3Cl3/Ba2I2F2/Tl3Cl3 and Sn2Te2/K2Br2/Sn2Te2 van der Waals heterostructures. These two heterostructures exhibit valley-selective linear dichroism, which enables the optical creation of interlayer or intralayer excitons with selected valley and electric polarization. Furthermore, both the K2Br2/Sn2Te2/K2Br2 and Sn2Te2/K2ClBr/Sn2Te2 heterostructures are ferrovalley materials due to the ferroelectricity of Sn2Te2 and the built-in electric field caused by Janus K2ClBr, respectively. Our results broaden the candidate VLC materials from 2D monolayers and bilayers to 2D van der Waals heterostructures.