  Intrinsic electron spin relaxation due to the D'yakonov-Perel' mechanism is
studied in monolayer Molybdenum Disulphide. An intervalley in-plane spin
relaxation channel is revealed due to the opposite effective magnetic fields
perpendicular to the monolayer Molybdenum Disulphide plane in the two valleys
together with the intervalley electron-phonon scattering. The intervalley
electron-phonon scattering is always in the weak scattering limit, which leads
to a rapid decrease of the in-plane spin relaxation time with increasing
temperature. A decrease of the in-plane spin relaxation time with the increase
of the electron density is also shown.
