Structural and anisotropic transport properties of (Hg,Re)Ba_2CaCu_2O_y vicinal films

摘要

Approximately 160-nm-thick (Hg_(0.9)Re_(0.1))Ba_2CaCu_2O_y [(Hg,Re)-1212] epitaxial thin films were fabricated on 2°-18.4°-tilt SrTiO_3 vicinal substrates with thin buffer layers. The vicinal films had superior crystallinity and superconducting properties comparable to those for conventional films with no tilt. X-ray diffraction measurements revealed that the tilt angles of the c axes of the (Hg,Re)-1212 are slightly larger by 0.5°-1.5° than the substrate tilt angles, which is attributed to deformation of crystal structure due to lattice mismatch in the c-axis direction. The resistivity and critical current density along the c-axis direction (ρ_c and J_(c-c)) were estimated to be ρ_c =500 mΩ cm at room temperature and J_(c-c) = (1.0-1.4) X 10~5 A/cm~2 at 10 K from transport measurements for different in-plane directions of the vicinal films. The ρ_c clearly exhibited semiconductor-like temperature dependence below 180 K. The temperature dependence of J_(c-c) almost agreed with the theoretical relationship for superconductor-insulator-superconductor junctions. The current-voltage characteristics in the directions across their a-b planes exhibited a multiple branch structure of intrinsic Josephson junctions with voltage jumps at intervals of approximately 20 mV at 4-40 K.