Effects of Nuclear Field Gradients on Spin Transport

Signatures of large nuclear fields, induced by the process of dynamic nuclear polarization, have been observed in spin transport and optical orientation experiments with n-GaAs [1,2,3]. In this work, the electron spin polarization is modeled using the spin drift-diffusion equation with various terms capturing the complex electron-nuclear spin dynamics in the system. For some boundary conditions, analytic solutions for the steady state polarization are ascertained for arbitrary applied field. Importantly, we extend the conventional spin drift-diffusion equation to include a term accounting for the nuclear field gradient which induces a spin-dependent force on the carriers. Experiments are proposed that would demonstrate the influence of nuclear field gradients on spin transport.

[1] M. Chan et al. Phys. Rev. B 80, 161206, (2009)

[2] N. J. Harmon, T. A. Peterson, C. C. Geppert, S. J. Patel, C. J. Palmstrøm, P. A. Crowell, and M. E. Flatté, Phys. Rev. B 92, 140201(R) (2015).

[3] Y.-S. Ou, Y.-H. Chiu, N. J. Harmon, P. Odenthal, M. Sheffield, M. Chilcote, R. K. Kawakami, and M. E. Flatté, Phys. Rev. Lett. 116, 107201 (2016).