Spin localization in Si:P—direct evidence fromP31NMR

Abstract

The normalized intensities of the ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ NMR spectra in Si:P decrease when the phosphorous content is lowered through the concentration ${\mathrm{n}}_{\mathrm{c}}$ for the metal-insulator transition. The ${}_{}{}^{31}{}_{}{}^{}\mathrm{P}$ NMR shift is maximum for ≃1.1${\mathrm{n}}_{\mathrm{c}}$ and becomes very small for n≃${\mathrm{n}}_{\mathrm{c}}$. For n≃1.2${\mathrm{n}}_{\mathrm{c}}$ electronic susceptibility χ on the observed nuclei does not follow the T variation of the macroscopic susceptibility but has all the characteristics expected for a Pauli electron gas. Already above ${\mathrm{n}}_{\mathrm{c}}$, disorder and correlations therefore induce spin localization on an inhomogeneous scale in uncompensated semiconductors.