One Dimensional Polaron Effects and Current Inhomogeneities in Sequential Phonon Emission

We have constructed a physical model to explain the tunneling current oscillations reported by Hickmott et. al. [Phys. Rev. Lett. 52, 2053] for GaAs/AlGaAs heterostructures in high magnetic fields. We propose that the periodic structure observed is due to space charge which builds up in the undepleted layer when electrons enter it with energy just below the phonon emission threshold. Such electrons interact with the lattice to form polarons whose energy is pinned to the phonon energy, and thus have a very small group velocity. The polaron effect is strongly enhanced by the confinement of the electrons by the strong magnetic field. We infer from the current-voltage data that most of the tunneling current flows through a small area of the sample. The combined model gives reasonable quantitative agreement with experiment.