  Two laterally adjacent quantum Hall systems separated by an extended barrier
of a thickness on the order of the magnetic length possess a complex Landau
band structure in the vicinity of the line junction. The energy dispersion is
obtained from an exact quantum-mechanical calculation of the single electron
eigenstates for the coupled system by representing the wave functions as a
superposition of parabolic cylinder functions. For orbit centers approaching
the barrier, the separation of two subsequent Landau levels is reduced from the
cyclotron energy to gaps which are much smaller. The position of the
anticrossings increases on the scale of the cyclotron energy as the magnetic
field is raised. In order to experimentally investigate a particular gap at
different field strengths but under constant filling factor, a GaAs/AlGaAs
heterostructure with a 52 Angstrom thick tunneling barrier and a gate electrode
for inducing the two-dimensional electron systems was fabricated by the cleaved
edge overgrowth method. The shift of the gaps is observed as a displacement of
the conductance peaks on the scale of the filling factor. Besides this effect,
which is explained within the picture of Landau level mixing for an ideal
barrier, we report on signatures of quantum interferences at imperfections of
the barrier which act as tunneling centers. The main features of the recent
experiment of Yang, Kang et al. are reproduced and discussed for different gate
voltages. Quasiperiodic oscillations, similar to the Aharonov Bohm effect at
the quenched peak, are revealed for low magnetic fields before the onset of the
regular conductance peaks.
