Synthetic Rashba spin-orbit system using a silicon metal-oxide semiconductor

The spin–orbit interaction (SOI), mainly manifesting itself in heavy elements and compound materials, has been attracting much attention as a means of manipulating and/or converting a spin degree of freedom. Here, we show that a Si metal-oxide- semiconductor (MOS) heterostructure possesses Rashba-type SOI, although Si is a light element and has lattice inversion symmetry resulting in inherently negligible SOI in bulk form. When a strong gate electric field is applied to the Si MOS, we observe spin lifetime anisotropy of propagating spins in the Si through the formation of an emergent effective magnetic field due to the SOI. Furthermore, the Rashba parameter α in the system increases linearly up to 9.8 × 10−16 eV m for a gate electric field of 0.5 V nm−1; that is, it is gate tuneable and the spin splitting of 0.6 μeV is relatively large. Our finding establishes a family of spin–orbit systems. Silicon is a light element with high lattice inversion symmetry, and so is not expected to possess a substantial spin–orbit interaction (SOI), which is desirable for spintronics. Here, a silicon-based heterostructure is demonstrated to have a gate-tuneable Rashba-type SOI.