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I will present two complementary examples of interference and interaction in low-dimensional systems. The first describes decoherence in an electronic Mach-Zehnder interferometer in the quantum Hall regime. At high temperature, the visibility decays exponentially with temperature. The corresponding energy scale depends nonmonotonically on magnetic field. Our data provide insight into the structure of edge states at the transition between two Hall plateaus.
The second example considers strongly disordered TiN thin films at the insulating side of the superconductor-insulator transition. Quantum-critical fluctuations in the transition region provide an intrinsic granular fine-structure of the superconducting order parameter, which leads to a Josephson network with a characteristic non-monotonic magnetoresistance. On the insulating side of the transition a peculiar state with unmeasurably small conductance is observed at very low temperatures, which breaks down above a certain threshold voltage. At higher temperature we find the usual hopping conductance. The magnetic field dependence of the activation energy and the threshold voltage can be understood in terms of the Josephson network model. |
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