Observation of Negatives-Wave Proximity Effect in Superconducting UBe13

The Josephson $I_c$ between a Ta-wire probe and an induced, surface, singlet, superconducting state in U${\mathrm{Be}}_{13}$ decreases with decreasing temperature below the bulk U${\mathrm{Be}}_{13}$ $T_c$, in contrast to the increase seen in comparison Mo samples. This shows that the bulk U${\mathrm{Be}}_{13}$ superconductivity suppresses the induced singlet superconductivity. Such suppression is evidence of a triplet super-conducting state in U${\mathrm{Be}}_{13}$. Evidence is presented for phase slip between weakly coupled singlet and triplet order parameters.