Break-junction tunneling spectra of Bi 2Sr 2CaCu 2O 8+ δ single crystals with temperature change

Abstract

Using a new method of the break-junction formation, the tunnel junctions with the extreme temporal resistance stability (0.003%) have been realized and investigated with the temperature change. Tunneling spectra of the Bi 2Sr 2CaCu 2O 8+ δ single crystals for the different kinds (rough and planar) of fracture surfaces have been studied. The reproducible gap-related peak 2 Δ P–P at ≈66 meV for a-direction tunneling goes to zero with the temperature rising faster in comparison with BCS theory, and the gapless 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 the single peak at 100–140 mV were observed. The peaks are supposed to be due to tunneling between CuO 2 and BiO layers and exhibit unusual temperature behaviour, giving the evidence of the temperature-dependent density of electron states in the BiO layers. The high bias effect on tunneling spectra has been investigated. The features observed are accounted for by the normal layer occurrence on the tunnel junction surfaces, Andreev reflection and proximity effect.