Josephson effects in long superconducting bridges with variable thickness

Abstract

We have studied the properties of long ( L≈20μm) superconducting threads (Pb or Sn) formed by pulse electrical breakdown in monocrystalline silicon. These long bridges with variable thickness have well defined d.c. and a.c. Josephson effects in large temperature range ( T/T c ⪆0.2 and 0.4 for Pb and Sn, respectively) and high magnetic fields (up to 0.14 T for Pb at 4.2 K). In the whole temperature range, the critical current has linear temperature dependence, as for “ideal” Josephson junctions. The results are interpreted by coherent motion of vortices. Some interesting results about satellites of quasiparticle gap structures and the asymmetry of these structures with respect to the current direction are presented.