Professor Roland Kawakami
Department of Physics and Astronomy
University of California, Riverside

Tunable spin transport at room temperature in single layer graphene

Abstract:

Graphene is an attractive material for spintronics due to the low intrinsic spin-orbit and hyperfine coupling, which should lead to excellent spin transport properties. Experimentally, graphene spin valves are the first gate-tunable material to exhibit spin transport at room temperature. This makes it a strong candidate for future spin-based logic applications. Devices exhibit a spin diffusion length on the order of 1-3 microns at room temperature, and the non-local spin signals as high as 70 ohms has been achieved in our laboratory. These favorable properties could be improved further by increasing the spin lifetimes (which are currently at typical values of 100 ps) by improving the material quality. Apart from the good performance characteristics, graphene also has unique properties which makes it an interesting system for studying spin-dependent phenomena. First the band structure has an electron-hole symmetry that typical semiconductors lack. This opens up some interesting possibilities regarding bipolar spintronic devices and the possible role of pn junctions on spin injection. Our studies find that the electron-hole symmetry for spin transport is obeyed at low bias, but the symmetry is broken at high bias. Second, the ultrathin nature of the graphene and its surface conduction allow for the modification of spin transport properties by controlled chemical doping. Our studies here have led to new insights on the origin of spin-relaxation in graphene spin valves. Third, the lack of large depletion regions allows one to control the spin injection and detection properties through atomic scale engineering of the ferromagnet/graphene interfaces. Our studies in this area investigate the role of engineered tunnel barriers on the efficiency of spin injection and detection. In this talk, I will discuss graphene spintronics in general, present some of our research results, and finally discuss the future prospects for the field.