Stacking-dependent exciton multiplicity in WSe$_2$ bilayers

TL;DR

This study investigates how stacking configurations in WSe$_2$ bilayers influence exciton properties, revealing stacking-dependent spectral multiplicity and exciton characteristics through combined experimental and theoretical approaches.

Contribution

It provides new insights into the impact of layer stacking on exciton multiplicity and optical properties in WSe$_2$ bilayers, supported by experimental data and beyond-DFT calculations.

Findings

Distinct optical features for 2H and 3R stackings.

Stacking affects exciton spectral multiplicity and phonon sidebands.

Theoretical calculations explain experimental observations.

Abstract

Twisted layers of atomically thin two-dimensional materials realize a broad range of novel quantum materials with engineered optical and transport phenomena arising from spin and valley degrees of freedom and strong electron correlations in hybridized interlayer bands. Here, we report experimental and theoretical studies of WSe$_2$ homobilayers obtained in two stable configurations of 2H ($60^\circ$ twist) and 3R ($0^\circ$ twist) stackings by controlled chemical vapor synthesis of high-quality large-area crystals. Using optical absorption and photoluminescence spectroscopy at cryogenic temperatures, we uncover marked differences in the optical characteristics of 2H and 3R bilayer WSe$_2$ which we explain on the basis of beyond-DFT theoretical calculations. Our results highlight the role of layer stacking for the spectral multiplicity of momentum-direct intralayer exciton transitions in absorption, and relate the multiplicity of phonon sidebands in the photoluminescence to momentum-indirect excitons with different spin valley and layer character. Our comprehensive study generalizes to other layered homobilayer and heterobilayer semiconductor systems and highlights the role of crystal symmetry and stacking for interlayer hybrid states.