Landau level crossing and pseudospin phase transitions in Si quantum wells

Magnetotransport properties are studied for a high mobility Si two-dimensional electron system by in situ tilting of the sample relative to the magnetic field. In contrast to the resistance spike in the quantum Hall regions, a pronounced dip in the longitudinal resistivity is observed during the Landau level crossing process for noninteger filling factors. Hysteresis behavior indicates that the transition from the conducting state to the insulating state, where the pseudospin is unpolarized, is the first-order phase transition.