Electron transport in mesoscopic structures

Recent advances in electron beam lithography have allowed to prepare high-quality metal structures with submicrometer dimensions. At low temperatures the size of these structures can become smaller than the coherence length over which the electrons maintain their phase memory. Therefore, a mesoscopic regime can be reached, where the quantum interference between conduction electron waves becomes important The interference effects can be conveniently tuned by applying a perpendicular magnetic field. Using a lift-off technique we have prepared various submicrometer Al and Au structures. In the superconducting Al loops the Ginzburg-Landau coherence length, which diverges near T-d corresponds to the relevant characteristic length scale. Due to their mesoscopic sample size the Al leaps behave as superconducting quantum interference devices (SQUIDs), even when no artificial Josephson junctions are present in the branches of the loop. The mesoscopic confinement of the superconducting wave function causes in addition anomalous Little-Parks oscillations of T-c when a magnetic field is applied. We have been able to further reduce the linewidth of the mesoscopic sample by using the tip of a scanning funneling microscope (STM) for local exposure of a very thin Langmuir-Blodgett layer used as an electron sensitive resist.