Abstract
A large number of tunneling measurements on ceramic monophasic Y 1 Ba 2 Cu 3 O 7−x samples with different oxygen content using the point-contact geometry was performed. After a deconvolution procedure for removing the thermal broadening, experimental data were analyzed by means of a model of the total tunneling current which contains two terms: A background "normal" tunneling current and a quasi-particle tunneling one. The quasi-particle current was expressed in terms of the lifetime broadening model. The dependence of the energy gap Δ and of the lifetime broadening parameter Γ, as determined by the model, on the temperature of the sample is discussed. A linear behaviour in the dependence of the gap on the critical temperature of the sample has been found. The ratio 2Δ/kT c varies between 4.3 and 7.2 depending on the value of T c which can be attributed to the sample surface. The possible presence of proximity effect in our tunneling experiments is also discussed.
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