Lifting
the valley degeneracy in two-dimensional transition metal
dichalcogenides could promote their applications in information processing.
Various external regulations, including magnetic substrate, magnetic
doping, electric field, and carrier doping, have been implemented
to enhance the valley splitting under the magnetic field. Here, a
phase engineering strategy, through modifying the intrinsic lattice
structure, is proposed to enhance the valley splitting in monolayer
WSe2. The valley splitting in hybrid H and T phase WSe2 is tunable by the concentration of the T phase. An obvious
valley splitting of ∼4.1 meV is obtained with the T phase concentration
of 31% under ±5 T magnetic fields, which corresponds to an effective
Landé geff factor of −14,
about 3.5-fold of that in pure H-WSe2. Comparing the temperature
and magnetic field dependent polarized photoluminescence and also
combining the theoretical simulations reveal the enhanced valley splitting
is dominantly attributed to exchange interaction of H phase WSe2 with the local magnetic moments induced by the T phase. This
finding provides a convenient solution for lifting the valley degeneracy
of two-dimensional materials.