Observation of negative s-wave proximity effect in superconducting UBe13

The Josephson Ic between a Ta-wire probe and an induced, surface, singlet, superconducting state in UBe13 decreases with decreasing temperature below the bulk UBe13 Tc, in contrast to the increase seen in comparison Mo samples. This shows that the bulk UBe13 superconductivity suppresses the induced singlet superconductivity. Such suppression is evidence of a triplet super-conducting state in UBe13. Evidence is presented for phase slip between weakly coupled singlet and triplet order parameters.