Tunneling conductance of break junction with the (100) plane fracture surface of Bi2Sr2CaCu2O8

Using the new method of breaking, the tunnel junctions with the (100) plane fracture surface could be obtained. The observed singularities in conductivity can be explained by tunneling between the different layers (CuO₂→CuO₂, sharp peaks at 2Δ _p−p =64±2mV;CuO ₂→BiO, peaks at 100–140 mV; BiO→BiO, wide maxima at about 250 mV). The tunneling spectra measured at T=4.2–100 K show that a shift of the 2Δ _p−p peak to lower biases is much stronger (from 64 to 37 mV) than the BCS prediction at T/T_c≤0.7. At higher T (up to T_c≈87K) the changes of the spectra look like those expected for gapless superconductivity in agreement with the ARPES data for a-direction.