Temperature dependence of the YBa2Cu3O7 energy gap in differently oriented tunnel junctions

We have applied the break-junction technique to highly biepitaxial c-axis oriented YBa2Cu3O7 thin films with TC (ρ=0) = 91 K. Mechanically adjustable junctions with a good stability and tunneling current favored along the ab-planes have been realized. The conductance characteristics of these junctions show the presence of gap related maxima that move towards zero bias for increasing temperatures. Considering the misorientation angle α≈ 45°± 5° of the junction, a maximum gap value at the Fermi level Δ≈ 22 meV is inferred at T = 13 K. The temperature dependence of the gap related structures, shows a quasilinear behavior for T > 0.4TC similar to that observed in c-axis oriented, S-I-N type YBa2Cu3O7 planar junctions.