Spin-polarized transport in F/S nanojunctions

We study spin-dependent electronic transport across ferromagnet/superconduc tor ballistic junctions modeled using tight-binding Hamiltonians with s, p and d orbitals and material-specific parameters. The first result of this p aper is that, by accurately modeling the band structure of the bulk materia ls, one can reproduce the measured differential conductance of Cu/Pb nanoco ntacts(1,2). In contrast the differential conductance of Co/Pb contacts can only be reproduced if an enhanced magnetic moment is present at the interf ace. The second result concerns the reliability of a method proposed in Ref s. 1-3 for determining the degree of polarization of a ferromagnet. By fitt ing the material-specific differential conductance curves to curves calcula ted using a single-band model we show that this method does not yield relia ble values for polarization and spin-dependent transmission.