Effects of a Parallel Magnetic Field on the Metal-Insulator Transition in a Dilute Two-Dimensional Electron System

Abstract

The temperature dependence of conductivity $\ensuremath{\sigma}(T)$ of a two-dimensional electron system in silicon has been studied in parallel magnetic fields $B$. At $B\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$, the system displays a metal-insulator transition at a critical electron density ${n}_{c}(0)$, and $d\ensuremath{\sigma}/dT>0$ in the metallic phase. At low fields ( $B\ensuremath{\lesssim}2\mathrm{T}$), ${n}_{c}$ increases as ${n}_{c}(B){\ensuremath{-}n}_{c}(0)\ensuremath{\propto}{B}^{\ensuremath{\beta}}$ ( $\ensuremath{\beta}\ensuremath{\sim}1$), and the zero-temperature conductivity scales as $\ensuremath{\sigma}({n}_{s},B,T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0)/\ensuremath{\sigma}({n}_{s},0,0)\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}f({B}^{\ensuremath{\beta}}/{\ensuremath{\delta}}_{n})$, where ${\ensuremath{\delta}}_{n}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}[{n}_{s}{\ensuremath{-}n}_{c}(0)]{/n}_{c}(0)$ and ${n}_{s}$ is electron density, as expected for a quantum phase transition. The metallic phase persists in fields of up to 18 T, consistent with the saturation of ${n}_{c}$ at high fields.