Unequivocal Determination of Spin-Triplet Superconductivity Using Composite Rings

Phase-sensitive measurements on a composite ring made of a superconductor of interest connected by a known singlet $s$-wave superconductor can unambiguously determine its pairing symmetry. In composite rings with epitaxial $\beta -$Bi${}_2$Pd and $s$-wave Nb, we have observed half-integer quantum flux when Nb is connected to the opposite crystalline ends of $\beta -$Bi${}_2$Pd and integer-quantum flux when Nb is connected to the same crystalline ends of $\beta -$Bi${}_2$Pd. These findings provide unequivocal evidence of odd-parity pairing state of the triplet superconductor $\beta -$Bi${}_2$Pd.