  The integration of the spin degree of freedom in charge-based electronic
devices has revolutionised both sensing and memory capability in
microelectronics. Further development in spintronic devices requires electrical
manipulation of spin current for logic operations. The approach followed so
far, inspired by the seminal proposal of the Datta and Das spin modulator, has
relied on the spin-orbit field as a medium for electrical control of the spin
state. However, the still standing challenge is to find a material whose
spin-orbit-coupling (SOC) is weak enough to transport spins over long
distances, while also being strong enough to allow their electrical
manipulation. Here we demonstrate a radically different approach by engineering
a heterostructure from atomically thin crystals, which are "glued" by weak van
der Waals (vdW) forces and which combine the superior spin transport properties
of graphene with the strong SOC of the semiconducting MoS$_{2}$. The spin
transport in the graphene channel is modulated between ON and OFF states by
tuning the spin absorption into the MoS$_{2}$ layer with a gate electrode. Our
demonstration of a spin field-effect transistor using two-dimensional (2D)
materials identifies a new route towards spin logic operations for beyond CMOS
technology.
