Superconducting lead nanobridges under magnetic fields

We discuss recent experiments on the properties of superconducting bridges of Pb of nanoscopic dimensions fabricated by a scanning tunneling microscope (STM). The bridges behave as weak links of variable dimensions whose form and smallest contact radius can be varied in situ. We find that these structures have upper critical fields several times the bulk critical field of Pb, forming at large fields an N-s-junction-s-N system. We discuss in this paper the method of fabrication and characterization of the studied bridges and we present results for three conduction regimes. (C) 2000 Elsevier Science B.V. All rights reserved.