The spatial distribution of the differential conductance for ultrathin Pb films grown on Si(111)7×7 substrate is studied by means of low-temperature scanning tunneling microscopy and spectroscopy. The formation of the quantum-confined states for conduction electrons and, correspondingly, the appearance of local maxima of the differential tunneling conductance are typical for Pb films; the energy of such states is determined mainly by the local thickness of Pb film. We demonstrate that the magnitude of the tunneling conductivity within atomically flat terraces can be spatially nonuniform and the period of the small-scale modulation coincides with the period of Si(111)7×7 reconstruction. For relatively thick Pb films we observe large-scale inhomogeneities of the tunneling conductance, which reveal itself as a gradual shift of the quantized levels at a value of the order of 50 meV at distances of the order of 100 nm. We believe that such large-scale variations of the tunneling conductance and, respectively, local density of states in Pb films can be related to presence of internal defects of crystalline structure, for instance, local electrical potentials and stresses.

We experimentally demonstrate that a thin dirty superconducting (S) strip covered by low resistive normal metal (N) approaches closer to the depairing current than a single S strip, which makes its non-linear properties stronger. The obtained result comes from proximity-induced superconductivity in the N layer, its large contribution to the superconducting properties of the SN bilayer and larger sensitivity to the current than that of the host S layer. We argue that such an SN bilayer could be a promising system for different applications based on the current-dependent kinetic inductance. In addition, we also find that in the presence of the N layer the maximal vortex velocity in the resistive state considerably increases.

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