Zero-bias conductance vanishing induced by the same-spin-band Andreev reflection in half-metallic ferromagnet/superconductor contacts

The Blonder-Tinkham-Klapwijk approach is extended to study conductance spectra of half-metallic ferromagnet/s-wave superconductor contacts. It is found that a distinct Andreev reflection (AR) does exist in which the incident electron and the Andreev-reflected hole belong to the same-spin subband, provided that spin-flip scattering is present at the interface. The predicted distinguishing mark of the same-spin-band AR is the zero-bias conductance vanishing and finite V-shape conductance within the energy gap. Its experimental observation will provide a conclusive proof for the same-spin-band AR and also a best judgement about the half-metallic ferromagnet.