Abstract
We have systematically studied the structural change and properties of intrinsic Josephson junctions in (Bi1−xPbx)2Sr2CaCu2Oy single crystals with x between 0 and 0.25. The single crystals were grown by a self flux method and characterized by using X-ray diffraction, electron diffraction and electron microscopy. The critical temperatures of the as-grown single crystals were 80∼90 K. It was successfully confirmed that the single crystals with x<0.2 have the orthorhombic structure with an incommensurate modulation, and the periodicity of the modulation increases and the c-lattice parameter decreases with increasing Pb content, while those with x>0.2 have the pseudotetragonal structure without any modulation structure. For the c-axis transport measurements, mesas were fabricated on the single crystals using photolithography and ion milling techniques. The results clearly showed that mesas for all x between 0 and 0.25 behave like stacks of superconductor-insulator-superconductor Josephson tunnel junctions. From the area dependence of critical current, it was found that the Josephson penetration depth of the intrinsic Josephson junctions in Bi2Sr2CaCu2Oy single crystals is ∼15 μm. Moreover, the critical current densities of the intrinsic Josephson junctions increased with x. This was interpreted by the variation of barrier property and decrease in structural modulation in (Bi1−xPbx)2Sr2CaCu2Oy single crystals depending on x.
