Magnetic impurities on superconducting Pb surfaces

It has been predicted theoretically and found experimentally that magnetic impurities induce localized bound states within the superconducting energy gap, called Yu-Shiba-Rusinov (YSR) states. Combining symmetry analysis with experimental findings provides a convincing argument for the energy splitting and distribution of the YSR peaks, but the full details of the electronic structure remain elusive, and simple models with point scatterers lack the full orbital complexity required to meet this challenge. In this paper, we combine a Green's function-based first-principles method, which incorporates a phenomenological parametrization of the superconducting state, with orbitally complex impurity potentials to make material-specific predictions of realistic systems. We study the effect of 3d transition elements on the superconducting energy gap of a Pb (001) surface. Not only do we find good agreement with experiment, we also show that the energetic position, strength, and orbital composition of the YSR states depend strongly on the chemical makeup of the impurity and its position with respect to the surface. Such quantitative results cannot be derived from simplified models but require full material-specific calculations.