Figure 3: Quasiparticle spectra.

Differential conductance spectra of the superconducting densities of states for the two different Al tips on an Al(100) sample (the tip wire diameters are 0.25mm in (a) and 1mm in (b)). To suppress subgap features, we have measured at low transmission (stabilization at 2 meV and 50 pA). The fits are shown as black lines with excellent agreement. The superconducting density of states of both tip and sample was modeled by the simple Bardee–Cooper–Schrieffer (BCS)-model without any additional broadening parameters.