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 ωi 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 ωs, where ωs−ωi = ±gμsH0/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 Yafetl 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.