Energy gap reduction in superconducting tin films by quasiparticle injection

摘要: In Sn-I-Sn-I-Pb tunneling structures the energy gap ~Sn of Sn is reduced by quasiparti­ cle injection via single-particle between films. as function quasiparticle density probed Pb contact and found in agreement with theory OWen Scalapino. An instability observed at critical reduction ratio predicted this for a first-ortler phase transition. Nonequilibrium distributions superconductors can be produced photonl - 3 phonon4 irradiation or 5 tunneling. Under constant conditions stationary distribution determined primary excitation rates, dependence relaxation recombination probabilities, secon­ dary pair-breaking rates phonon absorption. Since phonons are emitted decay, escape probability from superconducting film into substrate intrinsic decay also have strong influence on quasi­ particle distribution. Whereas gener­ al problem solved numerically,6 two important simple models been discussed past: For limit lifetimes long compared to times, Owen Scalapino7 pro­ posed nonequilibrium which excess number quasiparticles characterized chemical potential p* > 0 their unperturbed lat­ tice temperature T. most films show high trappingS pairbreaking, Parker9 proposed model an elevated T* T describes particles A signifi­ cant difference that "/1* model" predicts first-order transi­ tion in­ creased, whereas "T* does not. Dif­ ferent experiments optical qua­ siparticles 2,3.1o did not give clear evidence fa­ vor one models. communication we report probing population contact. ac­ cord 11-* find stronger than thermal case observe reduction. The sample consists overlapping film, width thickness each being 1.4 mm 1000 A, respectively (Fig. 1). Silicon single crystals used substrates cooled direct liquid­ He bath backside. front surface Sn-J-Sn-J-Pb structure kept under vac­ uum exposed liquid He. By 15-min glow-discharge oxidation O2 100 mTorr resistance Sn-J-Sn junctions re­ sulted higher voltage asymptotic value R",,?25 mn. Sn-J-Pb typical values Roo'" 1 increased was necessary obtaining popu­ lation currents below cur­ rents structure. This allows bat­ tery voltages energies multiples suc­ cessive relaxation-phonon emission reabsorp­ pairbreaking increaSing effective rate excitations. Using conventional electronic measuring tech