Resistance of superconducting-normal interfaces

摘要: The work of Pippard, Shepherd & Tindall (P. S. T.) on the resistance copper foil sandwiched between superconducting lead electrodes has been extended (1) to study influence alloying with bismuth, (2) investigate other pairs metals, Pb-Re, Pb-Mo, Pb-Al, Pb-Sn, Sn-Al. In addition, different techniques for depositing have investigated; evaporation in vacuo after cleaning surface by sputtering found give most consistent results and minimal oxide contamination at metallic interface. Thin layers rise a characteristic sandwich as temperature is lowered well below transition. behaviour fairly simple model which regions contact carry current parallel tunnel junctions; conductivity latter much higher than used experiments tunnelling, it conjectured that they are monomolecular. towards transition lead, observed P. T., becomes more marked when bismuth added but reaches limiting 5 % Bi maintained up 20 Bi, point less reproducible, might be expected two phase electrode. lowest temperatures also somewhat increased addition lead. A theory observations developed extension argument T. attributes extra penetration excitations from normal metal into superconductor, provided an energy above gap. With these frequently scattered before finally being assimilated equilibrium state, scattering reveals itself resistance. At no can enter superconductor metal, if were pure perfect total reflexion reversal character, analysed Andreev, would reflected excitations, however, penetrate something like coherence length form evanescent mode. It mode impurities responsible partial without change hence low temperatures. process modes some detail problem developing full three dimensional case discussed final conclusion. one nevertheless capable complete solution, though reasons given not trusting its predictions real situation. Although fully quantitative explanation experimental possible either or near (in because effects due short lifetime lead), qualitative agreement models experiment unsatisfactory. sandwiches centre part lower flanking confirm showing how begins drop falls temperature. Pb-Mo samples behave molybdenum had about 1K although samples, possibly iron content, 0.4 K.