Superconducting Properties of Epitaxial Yttrium BARIUM(2) COPPER(3) OXYGEN(7-DELTA) Thin Films and Yttrium BARIUM(2) COPPER(3) OXYGEN(7-DELTA)/PRASEODYMIUM BARIUM(2) COPPER(3) OXYGEN(7-Z)/YTTRIUM BARIUM(2) COPPER(3) OXYGEN(7 - Heterostructures Grown by Pulsed Laser Deposition
Abstract
The study of the intrinsic behavior of high transition temperature copper-oxide superconductors (HTSC) has proven to be challenging because of the extreme sensitivity of their transport properties on material quality. These compounds are characterized by a high degree of structural and electrical anisotropy, and a very short superconductive coherence length of the same order as the size of the crystalline unit cell (~5-30 A). As a result, microscopic defects such as oxygen vacancies, cationic disorder, and the presence of minute impurities have a significant effect on electrical transport in these materials. Therefore, much effort has been expended in synthesizing sizable samples that are homogeneous, well characterized, and emenable to the study of the anisotropic properties of the HTSC. We have demonstrated that thin films of HTSC compounds such as rm YBa_2Cu_3O_{7 -delta}, which is a 92 K superconductor, can be synthesized easily by a technique known as pulsed laser deposition, and display superconducting properties comparable to or better than those of bulk poly- or single -crystalline samples. Furthermore, we have shown that layer by layer film growth permits unprecedented control on the characteristics of the sample allowing precise artificial adjustment of sample, properties on the scale of one or two unit cells; for example, we have epitaxially grown rm YBa_2Cu_3O_{7-delta}/PrBa _2Cu_3O_{7-z}/YBa_ 2Cu_3O_{7-delta} heterostructures (where rm PrBa_2Cu _3O_{7-z} is a non-superconducting isomorph of rm YBa_2Cu_3O_ {7-delta}) with individual layer thicknesses of a few tens of angstroms. We have applied such artificially structured systems to the fabrication of Josephson weak-links, and have successfully and reproducibly observed both the dc and ac Josephson effects in these junctions. We have also demonstrated thin films grown with the perovskite copper-oxide planes oriented perpendicular to the film surface. In such films, the current carrying copper-oxide planes of the superconductor are not continuous but are arranged in a mosaic, allowing for the simultaneous flow of superconducting currents along the in-plane and out-of-plane directions of the film. On a scale > 1 mum, this results in a quasi -isotropic superconducting microstructure, and is a demonstration of the enormous potential that superconducting thin film heterostructures offer for investigating the phenomenon of high temperature superconductivity.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1992
- Bibcode:
- 1992PhDT.........5I
- Keywords:
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- YTTRIUM BARIUM COPPER OXIDE;
- PRASEODYMIUM BARIUM COPPER OXIDE;
- BARIUM COPPER OXIDE;
- Physics: Condensed Matter; Engineering: Materials Science; Engineering: Electronics and Electrical