Fig. 5: Increasing impurity-substrate coupling during tip approach.
a Series of differential conductance spectra (normalized) through an impurity with YSR state measured with a superconducting tip as function of tip-sample distance (z-position). The YSR states move (inner peaks), while the coherence peaks (BCS) do not (outer peaks). At closer distances, higher order phenomena (Josephson effect at zero voltage and multiple Andreev processes near the YSR states) are visible. b YSR state energy positions as function of tip-sample distance extracted from the data set in a. c Scaled impurity-substrate coupling calculated from the energies in b. d The reduced transmission \({\tau }_{\text{exp}}/{\tilde{\Gamma }}_{\text{t}}\) emphasizes the deviation of the experimental data τexp compared with the model with constant coupling τ0. We find good agreement with the branch τs, where the impurity-substrate coupling increases during the tip approach.
