Electrically induced shifts of the GaAs nuclear spin levels

Abstract

The application of a dc homogeneous electric field in a GaAs crystal will induce a quadrupolar splitting of the nuclear-spin levels. This splitting has been observed for $^{71}\mathrm{Ga}$, $^{69}\mathrm{Ga}$, and $^{75}\mathrm{As}$ using a pulsed NMR spectrometer. A constant (${R}_{14}$) that relates the coupling between the induced field gradient and the applied electric field has been measured. The values found were ${R}_{14}(\mathrm{Ga})=2.85\ifmmode\times\else\texttimes\fi{}{10}^{10}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ and ${R}_{14}(\mathrm{As})=3.16\ifmmode\times\else\texttimes\fi{}{10}^{10}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. These results are in disagreement with those from a similar experiment reported by Gill and Bloembergen. The measured values of ${R}_{14}$ were found to be independent of the applied electric field strength. The two-electron bond-orbital model developed by Huang, Moriarty, Sher, and Breckenridge has been used to interpret the experimental measurements. In evaluating the theory, a Hartree-Fock atomic $s{p}^{3}$ hybrid wave-function basis set is used to find the induced field gradient caused by the electrostatic distortion of the bond. With no adjustable parameters, the value of ${R}_{14}(\mathrm{As})$ calculated from the theory is smaller than the experimental number by a factor of 1.4, while the calculated ${R}_{14}(\mathrm{Ga})$ is a factor of 4 too small.