Lateral proximity effect and long-range energy-gap gradients in Ta/Al and Nb/Al superconducting tunnel junctions
Roland den Hartog, A. Golubov, P. Verhoeve, A. Poelaert, D. Martin, A. Peacock, A. van Dordrecht, D. J. Goldie
DOI 10.1103/PhysRevB.63.214507 · Physical Review B
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Abstract
We present the results of current-voltage characterizations of Nb/Al and Ta/Al superconducting tunnel junctions, which reveal a dependence of the measured energy gap on the size of the junction. This implies a geometrical dependence of the energy gap, which suggests that the effective local energy gap has a lateral spatial variation on a scale of several μm. An extended version of the theory of the proximity effect could explain this phenomenon when lateral coherence lengths are introduced, which are of the order of the bulk coherence length in Al. One of the consequences of this theory is that the coherence length in a thin film cannot be taken to be isotropic. Another is that the effective lateral coherence length, which features in the lateral Usadel equation, actually depends on the quasiparticle energy.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
| Ta Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
| Al Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | — | Pressure not reported | unknown |
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