Quantum Hall-insulator transitions in lattice models with strong disorder

We report results of numerical studies of the integer quantum Hall effect i n a tight-binding model on a two-dimensional square lattice with noninterac ting electrons, in the presence of a random potential as well as a uniform magnetic field applied perpendicular to the lattice. We consider field magn itudes such that:the area per flux quantum is commensurate with the lattice structure. Topological properties of the single electron wave functions ar e used to identify current carrying states that are responsible for the qua ntized Hall conductance. We study the interplay between the magnetic field and the disorder, and find a universal pattern with which the current carry ing states are destroyed by increasing disorder strength, and the system dr iven into an insulating state. We also discuss how to interpolate results o f lattice models to the continuum limit. The relationship to previous theor etical and experimental studies of quantum Hall insulator transitions in st rongly disordered systems at low-magnetic fields is discussed. [S0163-1829( 99)02911-2].