  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.
