Prof. Gernot Güntherodt, RWTH Aachen
Graphene is a most simple and perfect two-dimensional electron system. Great expectations have been raised for spin transport in graphene because of its small spin-orbit coupling and negligible hyperfine interaction. The response of pure spin currents in E-field free, non-local spin valve structures and in transverse magnetic fields (Hanle precession) allows to extract the spin transport parameters of graphene. The spin lifetime is found to scale with the contact resistance. However, the injection of spins into graphene via oxide tunnel barriers imposes limitations to the expected spin lifetime of > 1 µs, besides extrinsic spin-orbit effects due to charged impurities or adsorbates. Dedicated preparation of the interfaces between graphene and the substrate as well as the injection electrode has resulted in spin lifetimes of 4 ns and spin diffusion lengths of 10 µm at room temperature. The use of h-BN as substrate for graphene yields carrier mobilities exceeding 20,000 cm2/Vs 1. These results are encouraging for the development of spintronics devices based on pure spin currents. The latter are dissipationless under time reversal symmetry.
*Work supported by DFG Research Unit FOR 912.
1 M. Drögeler, F. Volmer, M. Wolter, B. Terrés, K. Watanabe, T. Taniguchi, G. Güntherodt, C. Stampfer, and B. Beschoten, Nano Lett. 14, 6050 (2014)