Anisotropy of the transport properties in YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (110) thin films
The anisotropy of the transport properties was studied systematically on high-quality epitaxial YBCO (110) thin-films obtained by both dc magnetron-sputtering and pulsed laser-ablation on single crystal (110) SrTiO{sub 3} substrates. These films have in-plane alignment of the c-axis of YBCO, which is essential to the transport study of the anisotropy between the ab-plane and the c-axis. Along the c-axis, {rho} shows a semiconductor-like upturn as T decreases and a metallic T-linear behavior along the Cu-O plane. This confirms the correlation between the semiconductor-like {rho} along the c-axis and slight oxygen-deficiency in YBCO. As point-defects are introduced into the thin-film by the 200 keV proton-irradiation, the {rho}-anisotropy dramatically changes. Along the Cu-O planes, these defects contribute only a residual {rho} as in normal metals. Along the c-axis, {rho} is significantly reduced. A `phase transition` from semiconductor-like to metal-like is completed at a low proton dose of 6 x 10{sup 14} ions/cm{sup 2}, where little effect is observed on T{sub c} and {rho}{sub ab}. This suggests that the unusual normal-state transport properties are irrelevant to the mechanism of HTS. In the superconducting state, the J{sub c,trans} has been measured as functions of T, H, and the direction of H. The T-dependence along the Cu-O plane fits the vortex-glass model while along the c-axis, it fits the Josephson tunnel-junction model. This observation implies that the extrinsic weak-link effect determines J{sub c,trans} along the c-axis. Similar measurements have also been conducted on YBCO a-, c-, and (113)-oriented thin films. Intrinsic pinning is the strongest pinning effect in YBCO despite the orientation of the film. J{sub c}-anisotropy in different field directions is due to the anisotropy of the pinning-effect. The surface pinning-effect is observed (for the first time) on YBCO.
- Research Organization:
- Houston Univ., TX (United States)
- OSTI ID:
- 50471
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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