• All states are localized in 2D
Strongly disordered systems
•
Even for a “dirty” sample, the localisation length of a 2DEG is of the order of a kilometer therefore the sample is effectively delocalised at zero magnetic field because of its finite size•
Therefore it is widely accepted that in order to observe insulator-quantum Hall transitions, one needs to deliberately introduce disorder so as toexperimentally realise a highly-disordered 2D system