Strong temperature dependence of the c-axis gap parameter of Bi2Sr2CaCu2O8+delta intrinsic Josephson junctions

Stacked series arrays of intrinsic Josephson tunnel junctions have been fabricated on the surfaces of Bi2Sr2CaCu2O8+delta single crystals using photolithography and Ar-ion milling together with in situ monitoring of the resulting current-voltage (I-V) characteristics. The number of junctions in the stack (along the c axis) is varied from 1-5 to similar to 200 in a controlled way. Both Josephson coupling and multiple branches with well developed gap features are seen in the I-V dependences of the arrays at T less than or similar to 90 K. The gap parameter Delta(c) is 10-13 meV at 4.2 K, which is approximately half the value reported in the literature. The temperature dependence of Delta(c) deviates strongly from the BCS one. Proximity induced superconductivity of the Bi-O layers may possibly explain both the reduced gap parameter and its temperature dependence.