Imaging spin diffusion in germanium at room temperature

The aim of spintronics is to exploit the spin degree of freedom to add new functionalities to electronic devices and boost their performances. Germanium is one of the most appealing materials for spintronic applications, thanks to its compatibility with the Si platform, the long electron spin lifetime, and the optical properties matching the conventional telecommunication window. Here, we implement a nonlocal spin injection/detection scheme in germanium at room temperature. The nonlocal geometry is particularly interesting in spintronics since it allows, in principle, spin manipulation in the channel between the spin injector and detector. By performing optical spin injection through a set of lithographically-defined metal microstrips, we demonstrate lateral spin transport in a lightly n-doped bulk Ge sample. Nonlocal spin detection is achieved using either magnetic tunnel junction or the inverse spin-Hall effect (ISHE) in a Pt stripe. With this setup, we directly map the spin diffusion in Ge, and, by combining optical spin orientation and the ISHE in Pt, we build a nonlocal spin-injection/detection scheme without the use of any ferromagnetic metal.