Josephson Phase Coherence and Coupling in High Tc Granular Superconductors
In order to understand the superconductive behaviour of the new high Tc superconductors, many experiments have been carried out. Among these, the measurements of a. c. complex susceptibility x = x′ + ix″ as a function of temperature are of great interestl. The in-phase component x′, corresponding to inductive variations, indicates perfect diamagnetism and flux shielding. The out-of-phase component x″, corresponding to resistive losses, can behave differently depending on which loss mechanism is involved. In the (RE) Ba2Cu3O7−δ oxides, the observed magnetic behaviour has been analyzed by several authors in terms of percolation, junctions, disorder or superconducting inclusions4,7 with the physical data apparently varying from one sample to another, depending on the synthesis methods and on the different heat treatments used. We have, therefore, performed inductive a. c. complex susceptibility as well as d. c. resistive measurements on sintered bulk and powdered samples of HoBa2Cu3O7−δ and on two types of YBa2Cu3O7−δ samples in order to correlate the resistivity, the morphology and the diamagnetic behaviour in these granular high Tc superconductors. The observed phenomena are directly dependent on the contact resistance between the grains (i. e. the ability of carrying supercurrent) and on the surface to volume ratio of the grains in a given material.
KeywordsContact Resistance Applied Magnetic Field Resistive Loss Diamagnetic Behaviour Sintered Bulk
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- 8.J. F. Beaudoin, F. Weiss, J. P. Senateur, T. Verhaege, P. Dubots, to be published at the Interlaken HTSC -M2S -Conference, March 1988Google Scholar