Andreev reflection spectroscopy on the heavy-fermion superconductor PrOs${}_4$Sb${}_{12}$: Microscopic evidence for multiple superconducting order parameters

Point-contact Andreev reflection spectroscopy was performed on single crystals of the heavy-fermion superconductor PrOs${}_4$Sb${}_{12}$, down to 90mK and up to 3Tesla. The conductance spectra showed multiple structures, including zero-bias peaks and spectral dips, which are interpreted as signatures of multiple pairing gaps, one clearly having nodes. Samples with 2% Ru replacing Os were also measured, showing pronounced spectral humps consistent with the emergence of a non-nodal gap. Detailed analysis of the spectral evolution revealed a magnetic field-\emph{vs.}-temperature phase diagram for PrOs${}_4$Sb${}_{12}$ characterized by two distinct superconducting order parameters.