Instability of the Two-Dimensional Metallic Phase to Parallel Magnetic Field

We report on magnetotransport studies of the unusual two-dimensional metallic phase in high mobility Si-MOS structures. We have observed that the magnetic field applied in the 2D plane suppresses the metallic state, causing the resistivity to increase dramatically by more than 30 times. Over the total existence range of the metallic state, we have found three distinct types of the magnetoresistance, related to the corresponding quantum corrections to the conductivity. Our data suggest that the unusual metallic state is a consequence of both spin- and Coulomb-interaction effects. Typeset using REVT E X Recently, convincing evidence for the existence of a 2D metallic state in Si-MOS structures at zero magnetic field has been obtained in studies of the quantum Hall effect to insulator transitions [1] and of the Global Phase Diagram [2]. The extended states, which in high magnetic field H are centred in the corresponding Landau bands, were found experimentally to merge and remain in a fi..