Magnetoconductance of metallic Si:B near the metal-insulator transition

The magnetoconductance of p-type Si:B samples with dopant concentrations just above the metal-insulator transition is negative (positive magnetoresistance) at all measured temperatures between 0.1 and 4.2 K and for magnetic fields up to 9 T. We attribute this to the effects of strong spin-orbit scattering associated with the valence bands in p-type materials. The magnetoconductivity varies as ${\mathit{H}}^2$ in small magnetic fields and approximately as ${\mathit{H}}^{1/2}$ at high fields, with deviations from this simple form which become increasingly significant as the metal-insulator transition is approached. Based on the assumption that the high-field magnetoconductance is attributable mainly to electron-electron interactions, a separation of the low-field magnetoconductance into components associated with interactions and localization yields a hole inelastic scattering rate ħ/${\mathrm{\tau }}_{\mathrm{in}}$ which varies approximately linearly with temperature.