▎ 摘　　要

We have performed spin and charge transport measurements in dual gated high mobility bilayer graphene encapsulated in hexagonal boron nitride. Our results show spin relaxation lengths lambda(s) up to 13 mu m at room temperature with relaxation times tau(s) of 2.5 ns. At 4 K, the diffusion coefficient rises up to 0.52 m(2)/s, a value five times higher than the best achieved for graphene spin valves up to date. As a consequence, lambda(s) rises up to 24 mu m with tau(s) as high as 2.9 ns. We characterized three different samples and observed that the spin relaxation times increase with the device length. We explain our results using a model that accounts for the spin relaxation induced by the nonencapsulated outer regions.