Controlling Spin Relaxation in Hexagonal BN-Encapsulated Graphene with a Transverse Electric Field

We experimentally study the electronic spin transport in hexagonal BN encapsulated single layer graphene nonlocal spin valves. The use of top and bottom gates allows us to control the carrier density and the electric field independently. The spin relaxation times in our devices range up to 2 ns with spin relaxation lengths exceeding 12 mu m even at room temperature. We obtain that the ratio of the spin relaxation time for spins pointing out-of-plane to spins in-plane is tau(perpendicular to)/tau(parallel to) approximate to 0.75 for zero applied perpendicular electric field. By tuning the electric field, this anisotropy changes to approximate to 0.65 at 0.7 V/nm, in agreement with an electric field tunable in-plane Rashba spin-orbit coupling.