Strain engineering of Rashba-Dresselhaus spin-orbit coupling and intrinsic spin-Hall effect in Si

The weak intrinsic spin-orbit coupling and centosymmetric crystal structure are critical bottleneck in development of Si spintronics because it leads to insignificant spin-Hall effect (spin current generation) and inverse spin-Hall effect (spin current detection) even though it results into long spin diffusion length at room temperature. In this experimental study, we use strain gradient to break the structural inversion symmetry, which causes flexoelectric effect and charge separation. This leads to the Rashba-Dresselhaus spin orbit coupling in the bulk of Si along with Si interface. The cubic Rashba-Dresselhaus spin-orbit coupling lifts the spin degeneracy of band structure introducing intrinsic spin-Hall effect, which is uncovered using spin-Hall magnetoresistance measurement in Ni₈₀Fe₂₀/MgO/p-Si freestanding thin film. The strain gradient effects are uncovered using piezoresistive behavior due to thermal expansion induced compressive stresses. The intrinsic spin-Hall effect is observed in both n-doped and p-doped Si thin films. This experimental study brings the Si spintronics closer to reality. This work demonstrates that strain gradient can be used for spin current generation, detection and control in Si.