Fig. 1: Anderson impurity model.
a In the Kondo impurity model, the YSR state arises owing to scattering from a spin-dependent impurity potential. b In the Anderson impurity model, the Yu-Shiba-Rusinov (YSR) state arises owing to hopping to and from an impurity state. c Energy diagram of the Anderson impurity model. The coupled impurity features an occupied state below the Fermi level at −EJ + EU and an unoccupied state above the Fermi level at EJ + EU, where EJ is the level splitting and EU is the level offset. Γs is the coupling strength. d Spectral functions of the two Anderson impurity states in the normal conducting state. There is significant overlap between these two states. e The resulting YSR states in the superconducting regime. Note the difference in energy scale between d and e. The spectra were calculated with a broadening parameter of γ = 10 μeV.
