Typical spectra of Ta–Ni (left panel) and (right panel) contacts at .
Differential resistance of two typical Cu–Ni contacts at (thick solid lines). Contact (a) has a rather small zero-bias anomaly, but one can clearly see the rise of the differential resistance at about due to electron-phonon interaction. Contact (b) has no resolvable electron-phonon interaction, but a huge zero-bias anomaly. The definition of , , and is shown. The zero-bias anomalies are fitted using Eqs. (1) and (2) with (thin solid lines). The Kondo voltage is (a) and (b), respectively.
Magnitude of the zero-bias anomaly as function of resistance for the indicated metal contacts. The spear-anvil type contacts have the two metals shown (like Ni–Ta). Break junctions are denoted by a single metal . For the Cu–Cu contacts we show the magnitude of the maxima (open symbols) as well as the minima (filled symbols). The measuring temperature was , except break junctions and point contacts . The thick solid lines are , as discussed in the text. Different symbols for the Ni–(Ta, Cu, Nb, Ni) data indicate different series of measurements, for example where the tip was freshly cut. No such distinction is made for the other contacts.
Full width at half maximum of the zero-bias anomaly as function of resistance for the indicated contacts. The same symbols as in Fig. 3 are used. The thick solid lines are , when the Kondo length equals the contact radius. The thin solid lines through the data points represent a 100-times larger Kondo length .
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