Two-Dimensional Metal in a Parallel Magnetic Field

We have investigated the effect of an in-plane parallel magnetic field [Formula presented] on two high mobility metalliclike dilute two-dimensional hole gas systems in GaAs quantum wells. The experiments reveal that, while suppressing the magnitude of the low temperature resistance drop, [Formula presented] does not affect [Formula presented], the characteristic energy scale of the metallic resistance drop. The field [Formula presented] at which the metalliclike resistance drop vanishes is dependent on both the width of the quantum well and the orientation of [Formula presented]. It is unexpected that [Formula presented] is unaffected by [Formula presented] up to [Formula presented] despite the fact that the Zeeman energy at [Formula presented] is roughly equal to [Formula presented].