Weak Levitation of 2D Delocalized States in a Magnetic Field

The deviation of the energy position of a delocalized state from the center of a Landau level is studied in the framework of the Chalker-Coddington model. It is demonstrated that the introduction of weak Landau level mixing results in an upward shift of the delocalized state in energy. The mechanism of a levitation is a neighboring-Landau-level-assisted resonant tunneling which ``shunts'' the saddle points. The magnitude of levitation is shown to be independent of the Landau level number.