Universal phase diagram of the floating up to quantum Hall extended state B → 0 and the possibility of a 2D metal

Full text: We investigate the relationship between the quantum Hall extended states in finite magnetic fields and the apparent metal-insulator transition at B = 0. Using extremely low density, high quality 2D GaAs electron systems (μpeak = 2.4 x 107 cm2V-1s-1) that exhibit an apparent MIT we show that even for magnetic fields as low as 0.02 T the extended states continue to float up in energy. This result is in agreement with previous studies of more disordered n-GaAs and p-SiGe where no metallic behaviour was observed at B = 0. However, in high quality p-GaAs samples which do exhibit an apparent 'metal'-insulator transition at B = 0 the authors have observed a saturation of the trajectory of the extended states as B → 0. In this work we provide an explanation as to why these studies have arrived at different conclusions and present a universal quantum Hall-insulator phase diagram that unifies the conflicting results