  Magnetic adsorbates on superconductors induce a Kondo resonance outside and
Yu-Shiba-Rusinov (YSR) bound states inside the superconducting energy gap. When
probed by scanning tunneling spectroscopy, the associated
differential-conductance spectra frequently exhibit characteristic bias-voltage
asymmetries. Here, we observe correlated variations of Kondo and YSR
asymmetries across an Fe-porphyrin molecule adsorbed on Pb(111). We show that
both asymmetries originate in interfering tunneling paths via a spin-carrying
orbital and the highest occupied molecular orbital (HOMO). Strong evidence for
this model comes from nodal planes of the HOMO, where tunneling reveals
symmetric Kondo and YSR resonances. Our results establish an important
mechanism for the asymmetries of Kondo and YSR lineshapes.
