Raman scattering from the bulk inactive out-of-plane B$^{1}_{2\text{g}}$ mode in few-layer MoTe$_{2}$

TL;DR

This study investigates the Raman scattering of the bulk-inactive out-of-plane B$^{1}_{2 ext{g}}$ mode in few-layer MoTe$_{2}$, revealing temperature-dependent resonance effects and a doublet structure in the spectra.

Contribution

It provides new insights into the resonance behavior and vibrational mode structure of few-layer MoTe$_{2}$, especially regarding the bulk-inactive out-of-plane mode.

Findings

Doublet structure observed in Raman spectra of tetralayer and pentalayer MoTe$_{2}$.

Enhanced Raman signals at low temperature under specific laser excitations.

Resonance with electronic states at the M point explains the observed effects.

Abstract

Raman scattering from the out-of-plane vibrational modes (A$_{1\text{g}}$/A'$_{1}$), which originate from the bulk-inactive out-of-plane B$^{1}_{2\text{g}}$ mode, are studied in few-layer MoTe$_{2}$. Temperature-dependent measurements reveal a doublet structure of the corresponding peaks in the Raman scattering spectra of tetralayer and pentalayer samples. A strong enhancement of their lower energy components is recorded at low temperature for 1.91 eV and 1.96 eV laser excitation. We discuss the attribution of the peaks to the inner modes of the respective Raman-active vibrations. The temperature evolution of their intensity strongly suggests a resonant character of the employed excitation, which leads to the mode enhancement at low temperature. The resonance of the laser light with the singularity of the electronic density of states at the $M$ point of the Brillouin zone in MoTe$_{2}$ is proposed to be responsible for the observed effects.