Second harmonic generation control in twisted bilayers of transition metal dichalcogenides

TL;DR

This study uses polarization-resolved second harmonic generation spectroscopy to measure and control the twist angle in MoS2/WSe2 heterostructures, revealing its impact on exciton resonances and nonlinear optical properties.

Contribution

It introduces a method to directly measure twist angles in TMD heterostructures using SHG spectroscopy and explores how twist angle influences exciton resonances.

Findings

Twist angle can be measured directly on assembled heterostructures.

SHG amplitude and polarization depend on twist angle and exciton resonances.

Near zero twist angle, exciton energies shift and new resonances appear.

Abstract

The twist angle in transition metal dichalcogenide (TMD) heterobilayers is a compelling degree of freedom that determines electron correlations and the period of lateral confinement of moir\'e excitons. Here we perform polarization-resolved second harmonic generation (SHG) spectroscopy of MoS2/WSe2 heterostructures. We demonstrate that by choosing suitable laser energies the twist angle between two monolayers can be measured directly on the assembled heterostructure. We show that the amplitude and polarization of the SHG signal from the heterostructure are determined by the twist angle between the layers and exciton resonances at the SH energy. For heterostructures with close to zero twist angle, we observe changes of exciton resonance energies and the appearance of new resonances in the linear and non-linear susceptibilities.