  Gated molybdenum disulphide (MoS2) exhibits a rich phase diagram upon
increasing electron doping, including a superconducting phase, a polaronic
reconstruction of the bandstructure, and structural transitions away from the
2H polytype. The average time between two charge-carrier scattering events -
the scattering lifetime - is a key parameter to describe charge transport and
obtain physical insight in the behavior of such a complex system. In this work,
we combine the solution of the Boltzmann transport equation (based on ab-initio
density functional theory calculations of the electronic bandstructure) with
the experimental results concerning the charge-carrier mobility, in order to
determine the scattering lifetime in gated MoS2 nanolayers as a function of
electron doping and temperature. From these dependencies, we assess the major
sources of charge-carrier scattering upon increasing band filling, and discover
two narrow ranges of electron doping where the scattering lifetime is strongly
suppressed. We indentify the opening of additional intervalley scattering
channels connecting the simultaneously-filled K/K' and Q/Q' valleys in the
Brillouin zone as the source of these reductions, which are triggered by the
two Lifshitz transitions induced by the filling of the high-energy Q/Q' valleys
upon increasing electron doping.
