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

The spin-orbit interaction (SOI), as a manifestation of a relativistic effect in solids, has been attracting great attention in condensed matter physics because of its abundant nature for manipulating and/or converting a spin degree of freedom. Compound materials with bulk inversion symmetry breaking (GaAs, BiTeI, NbSe2…), heterostructures consisting of the aforementioned materials (InGaAs/InAlAs, Bi/Ag…) and single heavy elements (Pt, W, Ta, Bi…) are pivotal material systems for generating strong Dresselhaus- and Rashba-type SOI and for shedding light on a wide variety of modern physics such as two-dimensional materials science, superconductivity, magnetoelectrics, spintronics etc. Consequently, however, light elements and materials with bulk inversion symmetry have been outside the scope of the quest for SOI in solids. In this work, we show that a Si metal-oxide-semiconductor (MOS) is a new material stage possessing Rashba-type SOI, although Si is a light element and has lattice inversion symmetry resulting in inherently negligible SOI in bulk form. A strong gate electric field is applied to the Si MOS, and unexpectedly, we observe spin precession of propagating spins in the Si through the formation of an emergent effective magnetic field due to the SOI in the Si MOS. 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, i.e., it is gate tuneable, and the spin splitting Δ0 (= 0.6 μeV) is equivalent to that in strained GaAs. This finding is a successful establishment of a synthetic Rashba system using a ubiquitous light element with bulk inversion symmetry and pioneers a new family of SOI systems.