Nonlinear Dispersion Relation and Out-of-Plane Second Harmonic Generation in MoSSe and WSSe Janus Monolayers

TL;DR

This study investigates the nonlinear optical properties of Janus monolayers MoSSe and WSSe, revealing their potential for advanced photonic applications through detailed harmonic generation measurements.

Contribution

It provides the first comprehensive mapping of the full second-order susceptibility tensor, including out-of-plane components, and measures third-order susceptibility in Janus monolayers.

Findings

Out-of-plane second harmonic generation observed.

Full susceptibility tensor mapped at various temperatures.

Resonance effects near exciton energies characterized.

Abstract

Janus transition metal dichalcogenides are an emerging class of atomically thin materials with engineered broken mirror symmetry that gives rise to long-lived dipolar excitons, Rashba splitting, and topologically protected solitons. They hold great promise as a versatile nonlinear optical platform due to their broadband harmonic generation tunability, ease of integration on photonic structures, and nonlinearities beyond the basal crystal plane. Here, we study second and third harmonic generation in MoSSe and WSSe Janus monolayers. We use polarization-resolved spectroscopy to map the full second-order susceptibility tensor of MoSSe, including its out-of-plane components. In addition, we measure the effective third-order susceptibility, and the second-order nonlinear dispersion close to exciton resonances for both MoSSe and WSSe at room and cryogenic temperatures. Our work sets a bedrock for understanding the nonlinear optical properties of Janus transition metal dichalcogenides and probing their use in the next-generation on-chip multifaceted photonic devices.