Nuclear Polarization in Homogeneous InSb by a Direct Current

Clark and Feher have shown that an electric field applied to InSb in a constant magnetic field produces nuclear polarization. Two mechanisms are suggested here to account for nuclear polarizations in homogeneous samples. In one mechanism, the kinetic temperatures of "spin up" and "spin down" electron distributions, ${{\theta }_R}^{+}$ and ${{\theta }_R}^{-}$, are assumed to be different. It is shown that a nuclear polarization of order $\frac{N^{+}}{N^{-}}\approx \left[\frac{{\tau }_N\left({{\theta }_R}^{-}\right)}{{\tau }_N\left({{\theta }_R}^{+}\right)}\right]\left[\frac{{\tau }_{\epsilon }\left({{\theta }_R}^{+}\right)}{{\tau }_{\epsilon }\left({{\theta }_R}^{-}\right)}\right]$ may be produced in this case. ${\tau }_N$ and ${\tau }_{\epsilon }$ are the nuclear and electronic longitudinal relaxation times ($T_1\text{'}\mathrm{s}$). In the second mechanism, the momentum distribution is assumed to be displaced by an amount $\Delta p$ due to the applied electric field. A nuclear polarization of order $\frac{\Delta p^2}{2m^{*}{E}_F}$ may be induced in this case. It is suggested that a sizable fraction of the nuclear polarization observed by Clark and Feher is due to the first of these mechanisms.