Response to parallel magnetic field of a dilute two-dimensional electron system across the metal-insulator transition

The response to a parallel magnetic field of the very dilute insulating two-dimensional system of electrons in silicon metal-oxide-semiconductor field-effect transistors is dramatic and similar to that found on the conducting side of the metal-insulator transition: there is a large initial increase in resistivity with increasing field, followed by saturation to a value that is approximately constant above a characteristic magnetic field of about 1 T. This is unexpected behavior in an insulator that exhibits Efros-Shklovskii variable-range hopping in zero field, and appears to be a general feature of very dilute electron systems.