Raman scattering and anomalous Stokes anti-Stokes ratio in MoTe2 atomic layers

TL;DR

This study investigates Raman scattering in MoTe2 layers, revealing all zone center optical phonons and their splittings, and discovers tunable anti-Stokes intensity enhancements linked to excitonic resonance effects.

Contribution

It provides the first detailed observation of all zone center phonons and their splittings in MoTe2, and uncovers tunable anti-Stokes Raman effects related to excitonic resonances.

Findings

All six zone center optical phonons observed with Davydov splittings.

Anti-Stokes intensity can surpass Stokes under certain conditions.

Resonance effects from C excitons influence Raman scattering.

Abstract

Stokes and anti-Stokes Raman scattering are performed on atomic layers of hexagonal molybdenum ditelluride (MoTe2), a prototypical transition metal dichalcogenide (TMDC) semiconductor. The data reveal all six types of zone center optical phonons, along with their corresponding Davydov splittings, which have been challenging to see in other TMDCs. We discover that the anti-Stokes Raman intensity of the low energy layer-breathing mode becomes more intense than the Stokes peak under certain experimental conditions, and find the effect to be tunable by excitation frequency and number of atomic layers. These observations are interpreted as a result of resonance effects arising from the C excitons in the vicinity of the Brillouin zone center in the photon-electron-phonon interaction process.