REPRODUCIBLE TUNNELING MEASUREMENTS IN CERAMIC Y1BA2CU3O7-X SAMPLES WITH DIFFERENT OXYGEN-CONTENT

A large number of tunneling measurements on ceramic monophasic Y1Ba2Cu3O7-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 DELTA and of the lifetime broadening parameter GAMMA, 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 2-DELTA/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.