  To date, a number of valley materials have been discovered with the
spin-valley or valley-layer couplings. It is highly desirable to realize the
interplay of more electronic degrees of freedom in a valley material. Based on
the first-principles calculations, we demonstrate the valley and spin
degeneracy liftings in the band structure of a TiSiCO monolayer, with the help
of the selective expression of the layer pseudospin via atomic adsorption. The
introduction of the transition-metal adatoms provides an effective electric
field and magnetic proximity effect, giving rise to the valley and spin
splittings. These splittings can be further tuned by applying an external
electric field. According to the modified band structure, various interlayer
excitons with different combinations of spins and electric dipoles are
selectively created, under the optical field of appropriate frequencies. The
tunable spin and valley splittings in atom adsorbed TiSiCO monolayer offer
opportunities for exploring the interactions between spin, valley and layer
pseudospin, and designing advanced optoelectronic devices.
