Raman scattering from the bulk inactive out-of-plane mode in few-layer MoTe₂

We report a study of Raman scattering in few-layer MoTe₂ focused on high-frequency out-of-plane vibrational modes near 291 cm^-1 which are associated with the bulk-inactive $$ mode. Our temperature-dependent measurements reveal a double peak structure of the feature related to these modes in the Raman scattering spectra of 4- and 5-layer MoTe₂. In accordance with literature data, the doublet's lower- and higher-energy components are ascribed to the Raman-active A_1g/$$ vibrations involving, respectively, only the inner and surface layers. We demonstrate a strong enhancement of the inner mode's intensity at low temperature for 1.91 eV and 1.96 eV laser light excitation which suggests a resonant character of the Raman scattering processes probed under such conditions. A resonance of the laser light with a singularity of the electronic density of states at the M point of the MoTe₂ Brillouin zone is proposed to be responsible for the observed effects.