  Van-der-Waals heterostructures have become a paradigm for designing new
materials and devices, in which specific functionalities can be tailored by
combining the properties of the individual 2D layers. A single layer of
transition metal dichalcogenide (TMD) is an excellent complement to graphene
(Gr), since the high quality of charge and spin transport in Gr is enriched
with the large spin-orbit coupling of the TMD via proximity effect. The
controllable spin-valley coupling makes these heterostructures particularly
attractive for spintronic and opto-valleytronic applications. In this work, we
study spin precession in a monolayer MoSe2/Gr heterostructure and observe an
unconventional, dramatic modulation of the spin signal, showing one order of
magnitude longer lifetime of out-of-plane spins (40 ps) compared with that of
in-plane spins (3.5 ps). This demonstration of a large spin lifetime anisotropy
in TMD/Gr heterostructures, is a direct evidence of induced spin-valley
coupling in Gr and provides an accessible route for manipulation of spin
dynamics in Gr, interfaced with TMDs.
