Umklapp-Enhanced Valley Drag in Moiré Bilayers

In moiré bilayers, the large lattice constant of the moiré superlattice makes the intralayer length scale notably larger than the interlayer separation, leading to non-trivial effects from interlayer interactions. This may include the formation of excitonic orders and other emergent interfacial phases. In this work, we investigate valley drag in moiré bilayers and show that it is strongly enhanced by interlayer umklapp scattering. In contrast to conventional uniform systems, such as GaAs-based two-dimensional electron gases or monolayer graphene, where the drag conductivity vanishes at first order in the interlayer interaction, for moiré bilayers, we find non-vanishing contributions. This suggests enhanced drag effects. Specifically, we show that interlayer umklapp processes enable a unique mechanism for valley drag. We propose an experimental setup, feasible with current state-of-the-art fabrication techniques, to detect and characterize this effect in moiré bilayer systems.