Electron spin lifetimes in long-wavelength Hg1-xCdxTe and InSb at elevated temperature

We have made direct pump-probe measurements of spin lifetimes in long-wavelength narrow-gap semiconductors at wavelengths between 4 and 10 \ensuremath{\mu}m and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes ${\ensuremath{\tau}}_{\mathrm{s}}\ensuremath{\sim}300\mathrm{ps}$ even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that ${\ensuremath{\tau}}_{\mathrm{s}}$ is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of ${\ensuremath{\tau}}_{\mathrm{s}}$ in nondegenerate lightly n-type ${\mathrm{Hg}}_{0.78}{\mathrm{Cd}}_{0.22}\mathrm{Te}$ of approximately the same bandgap as InSb and find that ${\ensuremath{\tau}}_{\mathrm{s}}$ varies from 356 ps at 150 K to 24 ps at 300 K. In this material lattice scattering dominates giving a ${T}^{\ensuremath{-}3/2}$ dependence for the mobility, and we expect a strong temperature dependence of ${\ensuremath{\tau}}_{\mathrm{s}}.$ There are two main models that have been invoked for describing spin relaxation in narrow-gap semiconductors: the Elliott-Yafet (EY) model which gives a ${T}^{\ensuremath{-}7/2}$ dependence of ${\ensuremath{\tau}}_{\mathrm{s}}$ in this limit and the D'yakonov-Perel model which gives a ${T}^{\ensuremath{-}3/2}$ dependence. Our results, both in magnitude and temperature dependence of ${\ensuremath{\tau}}_{\mathrm{s}},$ imply that the EY model dominates in these materials.