In combination with the strong spin-splittings, optical excitation with a laser of suitable polarization and energy allows to initiate the electron valley state (K + or K -) and its spin (up or down).
In combination with the strong spin-splittings, the spin and valley degree of freedoms are coupled, resulting stable valley polarization. Thanks to these properties, a laser of suitable polarization and energy allows to initiate the electron valley state (K + or K -) and its spin (up or down).