Observation of excitonic resonances in the second harmonic spectrum of MoS$_2$

TL;DR

This study measures the second-harmonic response of MoS$_2$ across a broad energy range, revealing excitonic features and linking experimental results with theoretical models to understand non-linear electron-hole pair excitation.

Contribution

It provides the first detailed experimental and theoretical analysis of second-harmonic spectra in multilayer MoS$_2$, connecting excitonic resonances with electronic structure.

Findings

Detection of A, B, and C excitonic resonances in SH spectrum

Good agreement between experimental data and theoretical simulations

Elucidation of non-linear electron-hole pair excitation mechanisms

Abstract

We measure the second-harmonic (SH) response of MoS$_2$ in a broad fundamental photon energy range between 0.85 and 1.7 eV, and present a continuous SH spectrum capturing signatures of both the fundamental A and B excitons in addition to the intense C resonance. Moreover, we interpret our results in terms of the first exciton simulation of the SH properties of multi-layered MoS$_2$ samples, represented by a study of trilayer MoS$_2$. The good agreement between theory and experiments allows us to establish a connection between the measured spectrum and the underlying electronic structure, in the process elucidating the non-linear excitation of electron-hole pairs.