Tunneling spectroscopy on Bi2Sr2CaCu2O8+δ single crystals at T = 4.2 K

Abstract We report on N-I-S point contact and S-I-S break junction tunneling measurements at T = 4.2 K on Bi 2 Sr 2 CaCu 2 O 8+δ single crystals ( T c = 78–86 K ). For the latter experiments, the breaking of the crystal was done in liquid He atmosphere in order to produce clean surfaces. The superconducting energy gap scales with T c within the error bars of the experiments. The S-I-S break junction on Bi 2 Sr 2 CaCu 2 O 8+δ single crystals identifies the direction of the tunneling current. The energy gap is found to be anisotropic: parallel to the CuO 2 -planes an average gap value of 2 δ ∥ = 45 ± 3 meV is obtained. Perpendicular to those planes the average gap value amounts to 2 δ ⊥ = 26 ± 3 meV. Hence, there results ratios of 2 δ ∥ (0) / k B T c = 5.9 ± 0.4 and and 2 δ ⊥ (0) / k B T c = 3.6 ± 0.5.