Fig. 1.  (Color online) (a) Schematic view of the A-type antiferromagnetic bilayer system with the perpendicular electric field shown in blue (positve) and red (negative). (b−d) The schematic spin- and layer-resolved density of states of the A-type antiferromagnetic bilayer system with the electric field normal to the van der Waals plane (b) E = 0 and (c) (d) E = E_c (E_c is the critical electric field for the emergence of half metallicity), in which 1-α(β) and 2-α(β) indicate the spin-α(β) channel in layer 1 and layer 2, respectively. The positive(negative) electric field induces the spin-α(β) electrons around the Fermi level. (e) The proposed spin field effect transistor model, in which the spin states in the channel are tuned by the gate voltage^[2].