Josephson effect in the unusual superconductors Lu₂Fe₃Si₅, LiTi₂O₄, and UBe₁₃

A Josephson supercurrent, which can be split by microwave photons of frequency ν into Shapiro steps of spacing ΔV = hν/2e, is expected between superconductors of like pairing type, either s- or p-wave. A weaker, and possibly unobservable effect, with step spacing Δ V 2 was predicted by Pals and van Haeringen between electrodes of unlike pairing type. Experiments using K-band microwaves and a Nb point contact have been carried out at 1.2 K on the d-band superconductors LiTi₂O₄ and Lu₂Fe₃Si₅. In both cases we find unambiguous indication of s-wave pairing, as in Nb. The same experiment on the heavy-fermion superconductor UBe₁₃ in the range 0.7-7 K also reveals steps of spacing ΔV. This indicates that UBe₁₃ has been induced into a state of s-wave superconductivity by proximity with the s-wave superconductors Nb.