Temperature and Electric Field Dependence of Spin Relaxation in Graphene on SrTiO3

The theoretically predicted intrinsic spin relaxation time of up to 1 mu s in graphene along with extremely high mobilities makes it a promising material in spintronics. Numerous experimental studies, however, find the spin lifetime in graphene to be several orders of magnitude below that theoretically predicted. Additionally, analyses of the spin relaxation mechanisms in graphene using conventional processes such as Elliot-Yaffet and D'yakonov-Perel' show a coexistence of both, with no clear dominance. Central to these experimental discrepancies is the role of the local environment including that of the underlying substrate. In this work, we use the electronically rich platform of SrTiO3 with broken inversion symmetry and study spin transport in graphene in the presence of surface electric fields. We find spin relaxation time and length as large as 0.96 +/- 0.03 ns and 4.1 +/- 0.1 mu m, respectively at 290 K in graphene, using non-local spin valve studies and find a non monotonous dependence with temperature, unlike that observed in other substrates. Analysis of the temperature dependence indicates the role of surface electric dipoles and electric field driven electronic and structural phase transitions unique to SrTiO3 for spin transport and spin relaxation in graphene.