Spin and Charge Drift Diffusion in Presence of Controllable Magnetic Field Gradients

While magnetic field gradients are well known to cause spin separation via the Stern Gerlach effect, the utilization of these gradients to induce spin currents in solid state systems has led to only a handful of investigations [1,2,3]. In this work, the spin polarization and charge dynamics are modeled by developing a set of spin drift-diffusion equations for a generic inhomogeneous field. Under certain geometries, Lorentz forces and Larmor precession can be avoided which is gives rise to analytic solutions. We focus primarily on the simple constant gradient magnetic field; under conditions of spin injection in a semiconductor, a charge current is induced by the gradient. The effects of spin relaxation and electric field are also considered. The theory of spin diffusion length under conditions of drift and diffusion is modified to treat influence of magnetic field gradients.

[1] J. Fabian and S. Das Sarma, Phys. Rev. B 66, 024436 (2002)

[2] M. Kodha et al., Nature Communications 3, 1082 (2012)

[2] N. J. Harmon and M. E. Flatté, Phys. Rev. B 106, 054207 (2022)