Observation of Odd-Parity Superconductivity with the Geshkenbein-Larkin-Barone 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 $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Bi}}_{2}\mathrm{Pd}$ and $s$-wave Nb, we have observed half-integer-quantum flux when Nb is connected to the opposite crystalline ends of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Bi}}_{2}\mathrm{Pd}$ and integer-quantum flux when Nb is connected to the same crystalline ends of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Bi}}_{2}\mathrm{Pd}$. With ascending temperature, the half-integer-flux quantization transits to integer-flux quantization, before the eventual loss of phase coherence. These findings point to odd-parity pairing symmetry in superconducting $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Bi}}_{2}\mathrm{Pd}$.