Umklapp-Enhanced Interlayer Valley Drag in Moir\'e Bilayers

TL;DR

This paper investigates interlayer valley drag in moiré bilayers, revealing a significant enhancement from umklapp scattering, which persists at low temperatures and is detectable with current fabrication methods.

Contribution

It demonstrates that umklapp scattering greatly enhances interlayer valley drag in moiré bilayers, a phenomenon that occurs at first order and remains at low temperatures, unlike conventional systems.

Findings

Interlayer valley drag appears at first order in interlayer interaction.

Umklapp scattering significantly enhances the drag effect.

The effect persists at low temperatures and is experimentally detectable.

Abstract

Van der Waals materials may be combined to form moir\'e patterns that are effectively crystal lattices. These systems are unique in that their in-plane unit cell sizes may be orders of magnitude larger than interlayer separations, leading to unique behaviors emerging from interlayer interactions. In this work, we investigate interlayer valley drag in lattice-matched moir\'e bilayers, demonstrating a remarkable enhancement due to umklapp scattering. In contrast to drag phenomena in more conventional two-dimensional systems, interlayer valley drag appears at first order in the interlayer interaction, and remains non-vanishing in the low temperature limit even at this low order in the interlayer coupling. We propose an experimental geometry, feasible with current state-of-the-art fabrication techniques, to detect and characterize this effect in moir\'e bilayer systems.