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TT: Tiefe Temperaturen
TT 4: Pinning und Vortexdynamik
TT 4.1: Hauptvortrag
Montag, 27. März 2000, 14:30–15:00, H18
The formation of strong pinning dislocations in epitaxial PLD YBCO films and their effect on the critical current density — •B. Dam, F.C. Klaassen, J. M. Huijbregtse, R. C. F. van der Geest, G. Doornbos, and R. Griessen — Faculty of Sciences, Division of Physics and Astronomy, Vrije Universiteit, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands
Identifying dislocations by means of chemical etching, we find that the high critical current densities in YBa2Cu3O7−δ thin films are due to strong pinning by these natural linear defects [1]. The dislocations are formed at the substrate-film interface and run uniformly through the whole film. We find that the magnetic field dependence of the critical current density jc is are characterised by a plateau upto a characteristic field B*. Above B*, jc decays exponentially. Measuring the dynamical relaxation rate (Q) we again find a plateau until B*. The characteristic field B* is proportional to the dislocation density. Hence, linear defects (both of edge and screw type) are the major strong pinning centres of our thin films. In contrast to the case of artificial linear defects produced in single crystals by irradiation, in our films we do not find a relaxation peak at B*. The decay of jc with temperature and field is poorly understood. We will present several strong pinning models illustrating this. We are able to tune the dislocation density by one order of magnitude by changing the deposition conditions. Secondary phases are in general a likely source for dislocations. It appears that in the first monolayers of YBa2Cu3O7−δ on SrTiO3 an anomolously high density of secondary phases is formed. Indeed, the density of these secondary phases scales with the deposition conditions and have the same degree of spatial order as the dislocations. [1] B.Dam et al., Nature 399 (1999) 439