Multifaceted moir\'e superlattice physics in twisted WSe$_2$ bilayers

TL;DR

This paper develops advanced models to understand the complex electronic and structural phenomena in twisted WSe₂ bilayers, revealing how lattice reconstruction and external factors influence moiré superlattice properties.

Contribution

It introduces hybrid $oldsymbol{k}oldsymbol{ imes}oldsymbol{p}$ tight-binding models for electrons and holes in twisted TMD bilayers, incorporating lattice relaxation, hybridisation, and piezoelectric effects, with applications to WSe₂.

Findings

Describes moiré effects in twisted WSe₂ bilayers with various configurations.

Shows influence of encapsulation, pressure, and electric fields on electronic properties.

Highlights the role of lattice relaxation and ferroelectric charge transfer.

Abstract

Lattice reconstruction in twisted transition-metal dichalcogenide (TMD) bilayers gives rise to piezo- and ferroelectric moir\'e potentials for electrons and holes, as well as a modulation of the hybridisation across the bilayer. Here, we develop hybrid $\mathbf{k}\cdot \mathbf{p}$ tight-binding models to describe electrons and holes in the relevant valleys of twisted TMD homobilayers with parallel (P) and anti-parallel (AP) orientations of the monolayer unit cells. We apply these models to describe moir\'e superlattice effects in twisted WSe${}_2$ bilayers, in conjunction with microscopic \emph{ab initio} calculations, and considering the influence of encapsulation, pressure and an electric displacement field. Our analysis takes into account mesoscale lattice relaxation, interlayer hybridisation, piezopotentials, and a weak ferroelectric charge transfer between the layers, and describes a multitude of possibilities offered by this system, depending on the choices of P or AP orientation, twist angle magnitude, and electron/hole valley.