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The differential resistances Rd= d V/d I(V) of point contacts between a normal metal and a caxis oriented YNi2B2C film (Tc= 15.2 K) in the superconducting (SC) state have been investigated. Rd(V) contains clear 'gap' features connected with processes of Andreev reflection at the boundary between a normal metal and a superconductor that allow the determination of the SC gap ? and its temperature and magnetic field dependence. A distribution of ? from ?min?1.5 meV to ?max?2.4 meV is revealed; however, the critical temperature Tcin all cases corresponded to that of the film. The value 2?max/kBTc?3.66 is close to the Bardeen-Cooper-Schrieffer (BCS) value of 3.52, and the temperature dependence ?(T) is BCS-like, irrespective of the actual ? value. It is supposed that the distribution of ? can be attributed to a gap anisotropy or to a multiband nature of the SC state in YNi2B2C, rather than to the presence of nodes in the gap.

We have studied thedV/dI vs.V characteristics of point contacts between the heavy fermion superconductor URu2Si2 and the conventional superconductors Zn and NbTi. Contacts between URu2Si2 and Zn do not show Josephson effects; instead Andreev reflection type structures occur, which are related to both, the heavy fermion and the conventional superconductor. In contrast, contacts between URu2Si2 and NbTi become superconducting at low currents. A closed-loop setup with two NbTi contacts on URu2Si2 showed SQUID oscillations in a small magnetic field. Our data give evidence that the contacts should be described as superconductor/normal/superconductor junctions with a thick normal layer on the URu2Si2 side of the contact with proximity induced superconductivity in theN-layer in the case of NbTi. With such a model the occurrence or absence of superconductivity can be explained and also the suppression of Andreev-scattering which is frequently observed for contacts between heavy fermion superconductors and normal metals.

The current-voltage characteristics of point contacts with the heavy-fermion compounds CeB6 and CeCu6 have been investigated in magnetic fields up to 20 T. An applied voltage over the contact leads to local heating of the contact area, which explains the observed deviations from Ohm's law. Using Cu as a counterelectrode, the hot spot at the contact allows the direct measurement of the temperature dependence of the thermopower.

We have performed a series of point-contact experiments, i.e. measurements of the voltage-dependent differential resistance, on single crystals of the heavy-fermion metal URu2Si2, which is both antiferromagnetic and superconducting, in the temperature range between 0.8 and 20 K. Our most important results are strong anomalies due to the antiferromagnetism belowTN=17 K. These anomalies appear to be composed of parts fitting into a selfheating model and other, possibly spectroscopic parts. A unique, i.e. either thermal or ballistic model thus seems to be inadequate for the description of these point-contacts. In the characteristics of high-ohmic contacts we find zero-bias maxima of a width comparable to the width of a charge- or spin-density wave gap found in specific heat measurements. For the superconducting state belowTc=1.3 K, our measurements indicate a zone of strongly suppressed superconductivity near the surface.