  Single layers of MoS2 and MoSe2 were optically pumped with circularly
polarized light and an appreciable polarization was initialized as the pump
energy was varied. The circular polarization of the emitted photoluminescence
was monitored as function of the difference between the excitation energy and
the A-exciton emission at the K-point of the Brillouin zone. Our results show a
threshold of twice the LA phonon energy, specific to the material, above which
phonon-assisted intervalley scattering causes depolarization. In both materials
this lead to almost complete depolarization within ~100 meV above the threshold
energy. We identify the extra kinetic energy of the exciton (independent of
whether it is neutral or charged) as the key parameter for presenting a
unifying picture of the depolarization process.
