  The fate of the current carrying states of a quantum Hall system is
considered in the situation when the disorder strength is increased and the
transition from the quantum Hall liquid to the Hall insulator takes place. We
investigate a two-dimensional lattice model with spatially correlated disorder
potentials and calculate the density of states and the localization length
either by using a recursive Green function method or by direct diagonalization
in connection with the procedure of level statistics. From the knowledge of the
energy and disorder dependence of the localization length and the density of
states (DOS) of the corresponding Landau bands, the movement of the current
carrying states in the disorder--energy and disorder--filling-factor plane can
be traced by tuning the disorder strength.
  We show results for all sub-bands, particularly the traces of the Chern and
anti-Chern states as well as the peak positions of the DOS. For small disorder
strength $W$ we recover the well known weak levitation of the critical states,
but we also reveal, for larger $W$, the strong levitation of these states
across the Landau gaps without merging. We find the behavior to be similar for
exponentially, Gaussian, and Lorentzian correlated disorder potentials. Our
study resolves the discrepancies of previously published work in demonstrating
the conflicting results to be only special cases of a general lattice model
with spatially correlated disorder potentials.
  To test whether the mixing between consecutive Landau bands is the origin of
the observed floating, we truncate the Hilbert space of our model Hamiltonian
and calculate the behavior of the current carrying states under these
restricted conditions.

Mesoscale and Nanoscale Physics