Multidimensional Triple Sum-Frequency Spectroscopy of MoS2 and Comparisons with Absorption and Second Harmonic Generation Spectroscopies

TL;DR

This paper demonstrates the first application of multidimensional triple sum-frequency spectroscopy to MoS2, revealing unique insights into its electronic states and validating previous band nesting interpretations.

Contribution

It introduces TSF spectroscopy for semiconductors, providing a new method to analyze electronic states and compare with traditional spectroscopies.

Findings

TSF spectrum differs from absorption and SHG spectra

Joint density of states and transition moments were extracted

Validation of the band nesting origin of the C feature

Abstract

Triple sum-frequency (TSF) spectroscopy is a recently-developed methodology that enables collection of multidimensional spectra by resonantly exciting multiple quantum coherences of vibrational and electronic states. This work reports the first application of TSF to the electronic states of semiconductors. Two independently tunable ultrafast pulses excite the A, B, and C features of a MoS2 thin film. The measured TSF spectrum differs markedly from absorption and second harmonic generation spectra. The differences arise because of the relative importance of transition moments and the joint density of states. We develop a simple model and globally fit the absorption and harmonic generation spectra to extract the joint density of states and the transition moments from these spectra. Our results validate previous assignments of the C feature to a large joint density of states created by band nesting.