Effects of a parallel magnetic field on the metal-insulator transition in a dilute two-dimensional electron system

The temperature dependence of conductivity sigma(T) of a two-dimensional electron system in silicon has been studied in parallel magnetic fields B. At B = 0, the system displays a metal-insulator transition at a critical electron density n(c)(0), and dsigma/dT > 0 in the metallic phase. At low fields ( B less than or similar to 2 T), n(c) increases as n(c)(B) - n(c)(0) proportional to B-beta (beta similar to 1), and the zero-temperature conductivity scales as s sigma(n(s),B,T = 0)/sigma(n,0,0) = f(B-beta/delta(n)), where delta(n) = [n(s) - 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.