Anisotropic in-plane properties of (103)/(013) orientedYBa2Cu3O7−δthin films grown on exact and miscut (110)SrTiO3substrates

Abstract

${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) grows upon (110) oriented ${\mathrm{SrTiO}}_{3}$ substrates with two equivalent tilt orientations and exhibits regions of each $45\ifmmode^\circ\else\textdegree\fi{}$ tilt. If the substrate orientation is ``miscut'' from the exact (110) orientation, the two tilts are no longer energetically equivalent, enabling the fabrication of films with controllable tilt disorder. We have carried out a comparative study of (103)/(013) YBCO films deposited onto exact cut $(0\ifmmode^\circ\else\textdegree\fi{})$ substrates, and onto $3\ifmmode^\circ\else\textdegree\fi{}$ and $5\ifmmode^\circ\else\textdegree\fi{}$ miscut substrates where the proportion of minority tilt is about 5% and 2%, respectively. The two-temperature sputter growth process that has been developed yields films which are essentially free of the (110) orientation and which have normal-state resistivities ${\ensuremath{\rho}}_{001}$ comparable to ${\ensuremath{\rho}}_{a}$ for a high-quality single crystal. In the superconducting state the three classes of film each exhibit features characteristic of a phase transition for both the [001] and the orthogonal transport current directions. Data from the $0\ifmmode^\circ\else\textdegree\fi{}$ and $5\ifmmode^\circ\else\textdegree\fi{}$ films exhibit excellent scaling collapse over very wide ranges of temperature; data from the $3\ifmmode^\circ\else\textdegree\fi{}$ films scale somewhat less well. Surprisingly, the transition temperatures differ significantly between the two transport directions in the $0\ifmmode^\circ\else\textdegree\fi{}$ films at all magnetic fields investigated and in the $3\ifmmode^\circ\else\textdegree\fi{}$ films at higher fields. The nonuniversality of the scaling parameters, the very high values of the exponent z, and the dependence of the transition temperature on transport direction cast doubt on a conventional interpretation in terms of a vortex-glass melting transition. Studies of the Ohmic behavior of the $5\ifmmode^\circ\else\textdegree\fi{}$ films show an in-plane anisotropy which remains constant as the system passes from the normal state, through the superconducting flux flow regime to the Ohmic thermally activated flux creep region. This constancy is consistent with the anisotropy in the vortex damping being equal to the normal-state anisotropy.