Long Distance Spin Transport in High Mobility Graphene on Hexagonal Boron Nitride

We performed spin transport measurements on boron nitride based single layer graphene devices with mobilities up to 40 000 cm${^2}$V$^{-1}$s$^{-1}$. We could observe spin transport over lengths up to 20 {\mu}m at room temperature, the largest distance measured so far for graphene. Due to enhanced charge carrier diffusion, spin relaxation lengths are measured up to 4.5 {\mu}m. The relaxation times are similar to values for lower quality SiO$_2$ based devices, around 200 ps. We find that the relaxation rate is determined in almost equal measures by the Elliott-Yafet and D'Yakonov-Perel mechanisms.