Observation of Pure Spin Diffusion Without Charge Transport by Spin Flip Raman Scattering

Abstract

In spin flip Raman scattering (SFRS) incident light of wavevector ${{\vec{k}}_{i}}$ and frequency ω_i interacts via spin orbit coupling with spins in an external magnetic field H₀, producing a spin flip which scatters the light to wavevector ${{\vec{k}}_{s}}$ and frequency ω_s, where ω_s−ω_i = ±gμ_ßH₀/ħ. The ± signs refer respectively to the Stokes and anti-Stokes components and correspond to oppositely directed spin reversals. This process was first suggested by Yafet^l following a treatment by Wolff² of Raman scattering from Landau levels in a semiconductor. SFRS was first observed for conduction electrons in InSb³ where the very large g-value (~50) led to tuneable spin flip Raman lasers.⁴ It was first observed for bound donors in CdS by Thomas and Hopfield.⁵ SFRS has also been applied in a number of experiments to the study of velocities⁶ and diffusional motion of donor electrons in semiconductors.^7–9 The diffusional motion appears as a contribution Dq² to the SFRS linewidth. In these previous studies the Dq² term was related to the diffusion of charge, while in this paper we report the observation of spin diffusion arising from the exchange interaction between bound donors, without any charge transport.

Work performed at Bell Laboratories.