Magnetoconductance due to parallel magnetic fields in silicon inversion layers

A new anomalous magnetoconductance in parallel magnetic fields has been observed in a two-dimensional electron system formed in n-channel silicon field-effect transistors in fields up to 1.5 T and in a temperature range 1–4.2 K. The magnetoconductance is positive at electron concentrations $N_S$>2×${10}^{16}$ electrons/${\mathrm{m}}^2$ and has been interpreted as an effect of suppression of the weak-localization correction to the conductivity. The experiment deduces the presence of an electron random walk in the direction perpendicular to the Si-${\mathrm{SiO}}_2$ interface with the rms value δz≤2.1±0.15 Å. At lower electron densities the magnetoconductance changes sign and has a magnitude much larger than predicted by the current electron-electron interaction theory. The enhancement has been explained by including the spin fluctuations induced by disorder.