Spin pumping and spin-orbit effects in Ge (Conference Presentation)

The field of spintronics is based on the manipulation of the spin degree of freedom. It uses the carrier spin angular momentum as a basic functional unit in addition to the charge. The first requirement of a semiconductor-based spintronic technology is the efficient generation of spin-polarized carriers into the device heterostructure made of Si or Ge (the materials of mainstream microelectronics) at room temperature. In this presentation, we focus on the generation of a sizeable spin population into Ge by spin pumping. Spin pumping corresponds to the generation of a pure spin current in the Ge film by exciting the ferromagnetic resonance of an adjacent ferromagnetic electrode with microwaves. The pure spin current is then detected using spin-orbit based effects. Our aim is to understand the basic mechanisms of spin pumping into Ge as well as the spin-to-charge conversion by inverse spin Hall effect (ISHE, bulk effect) [1-4] and Rashba-Edelstein effect (interface effect) [5]. The influence of interface states is clearly demonstrated. Moreover, using the spin-split Rashba sub-surface states of the Ge(111) surface, we succeeded in demonstrating a giant conversion of a spin current generated by spin pumping into a charge current by the Rashba-Edelstein effect [6,7]. Our experimental findings are supported by ab-initio calculations. 1. Rojas-Sánchez, J.-C. et al. Spin pumping and inverse spin Hall effect in germanium. Phys. Rev. B 88, (2013). 2. Kato, Y. K., Myers, R. C., Gossard, A. C. and Awschalom, D. D. Observation of the spin Hall effect in semiconductors. Science 306, 1910–1913 (2004). 3. Valenzuela, S. O. and Tinkham, M. Direct electronic measurement of the spin Hall effect. Nature 442, 176–179 (2006). 4. Saitoh, E., Ueda, M., Miyajima, H. and Tatara, G. Conversion of spin current into charge current at room temperature: Inverse spin-Hall effect. Appl Phys Lett 88, 2509 (2006). 5. Bychkov, Y. A. and Rashba, E. I. Oscillatory effects and the magnetic susceptibility of carriers in inversion layers. Journal of Physics C: Solid State Physics 17, 6039–6045 (1984). 6. Edelstein, V. M. Spin polarization of conduction electrons induced by electric current in two-dimensional asymmetric electron systems. Solid State Communications 73, 233–235 (1990). 7. Rojas-Sánchez, J.-C. et al. Spin-to-charge conversion using Rashba coupling at the interface between non-magnetic materials. Nat Comms 4, (2013).