Break-junction tunneling spectra of Bi2Sr2CaCu2O8+delta single crystals with temperature change

Using a new method of the break-junction formation, the tunnel junctions wi th the extreme temporal resistance stability (0.003%) have been realized an d investigated with the temperature change. Tunneling spectra of the Bi2Sr2 CaCu2O8+delta single crystals for the different kinds (rough and planar) of fracture surfaces have been studied. The reproducible gap-related peak 2 D elta(P-P) at approximate to 66 meV for a-direction tunneling goes to zero w ith the temperature rising faster in comparison with BCS theory, and the ga pless superconductivity seems to be most probable at T --> T-c. The spectra with the two additional peaks (at 100-140 mV and about 250 mV) and with th e single peak at 100-140 mV were observed. The peaks are supposed to be due to tunneling between CuO2 and BiO layers and exhibit unusual temperature b ehaviour, giving the evidence of the temperature-dependent density of elect ron states in the BiO layers. The high bias effect on tunneling spectra has been investigated. The features observed are accounted for by the normal l ayer occurrence on the tunnel junction surfaces, Andreev reflection and pro ximity effect. (C) 1999 Published by Elsevier Science B.V. All rights reser ved.