DESTRUCTION OF INTEGER QUANTUM HALL-EFFECT AT STRONG DISORDER - A NUMERICAL STUDY

A breakdown of integer quantum Hall effect (IQHE) at strong disorder i s studied numerically in a lattice model. We find a generic sequence b y which the integer quantum Hall plateaus disappear: higher IQHE plate aus always vanish earlier than lower ones. We show that extended level s between these plateaus do not float up in energy but keep merging to gether after the disappearance of plateaus, which eventually leads to a localization in the whole system. We also study this phenomenon in t erms of topological property, which provides a simple physical explana tion.