DISAPPEARANCE OF INTEGER QUANTUM HALL-EFFECT

The disappearance of integer quantum Hall effect (IQHE) at strong diso rder and weak magnetic field is studied in a lattice model. A generic sequence by which the IQHE plateaus disappear is revealed: higher IQHE plateaus always vanish earlier than lower ones, and extended levels b etween those plateaus do not float up in energy but keep merging toget her after the destruction of plateaus. All of these features remain to be true in the weak-field limit as shown by the thermodynamic localiz ation-length calculation. Topological characterization in terms of Che rn integers provides a simple physical explanation and suggests a qual itative difference between the lattice and continuum models.