BREAK JUNCTION TUNNELING ON BI2SR2CACU2O8+DELTA-SINGLE CRYSTALS

Break junction tunnelling experiments on Bi2Sr2CaCu2O8+delta-single crystals were performed at different temperatures. Carefully adjusted samples exhibited conductance curves showing only one large peak at positive and negative bias voltages. From these measurements a gap value DELTA = (21.2 +/- 2.8) meV, i.e. 2-DELTA/k(B)T(c) = (5.5 +/- 0.8), was inferred. The behaviour of the conductance curves is similar to that of conventional superconductors but with a much larger broadening of the tunnelling characteristic. Therefore, several models which could explain this smearing are compared with the experimental data. However, it is found that none of them is capable of fitting the conductance curves convincingly. In some cases tunnel characteristics similar to those predicted by a charging effect model or a multigap model were obtained.