Anisotropic multiband superconductivity in Zn observed by simultaneous Andreev reflection and Yanson point-contact spectroscopy

Andreev reflection (AR) and Yanson point-contact spectroscopy (PCS) have been applied simultaneously to study the superconducting (SC) gap and the electron–phonon interaction (EPI) in a Zn single crystal. The correlation between SC gap value and EPI spectrum allowed us to establish the anisotropy of the SC gap. Evidence for multiband superconductivity in Zn is present with two gaps related as 1:1.3. We also found that the AR features are more robust against the point-contact quality than the EPI ones, possibly, due to the large coherence length in Zn compared to the typical PC size. Even for the PCs close to the ballistic regime with intense EPI spectra, the transmission coefficient evaluated from the AR spectra is near the one predicted theoretically for the diffusive regime of a current flow in the PC. Understanding those phenomena would provide a more reliable basis to apply both types of spectroscopies to study more complex SCs.