Tunneling junctions of the heavy-fermion superconductor UPd 2Al 3

Abstract

Tunneling spectroscopy on planar Giaever-type junctions is a powerful tool for the investigation of the superconducting state of metals. Since it is possible to prepare high-quality epitaxial thin films of the heavy-fermion compound UPd 2Al 3, this method can be used to examine the energy gap of this presumably unconventional superconductor. We prepared cross-junctions consisting of a UPd 2Al 3 base electrode and a metal counter electrode (Au, Al or Ag). These small area contacts without artificial barriers have only low junction resistances and suffer from irreproducibility. On the other hand, on some of those junctions we observed BCS-like tunneling conductivity. In order to increase the junction resistances AlO x or UO x were used as a artificial barrier with Al as a counter-electrode. As an alternative to quasi-particle tunneling, the preparation of Josephson-junctions could be an easier approach. A supercurrent between a small In-dot and an UPd 2Al 3 film was observed.