Pinning of Landau levels in open two dimensional electron systems

Electron tunnelling between two dimensional electron systems of different electron concentration in magnetic field normal to the layers have been studied. Parallel 2DES were separated from each other by Al0.3Ga0.7As barrier and from highly doped n(+)-GaAs contact regions by undoped GaAs-layers. In our samples each of the 2DES and adjacent contact region were in thermodynamic equilibrium provided by free carrier exchange. The measured I-V dependencies demonstrated pronounced resonant features arising when ground states of the 2DES's were adjusted by external bias. The magnetic field shifted resonant peak position. The shift on the voltage scale was linear versus magnetic field, but exhibited discontinuity in particular magnetic fields. The Landau levels pinning in the 2DES's by chemical potential in the contact region explains the experimental findings.