Paramagnetic Meissner effect in high-temperature superconductors: Experiments and interpretation

Abstract

The results are presented of experiments on the paramagnetic Meissner effect, the appearance of a net paramagnetic moment when some high-temperature superconductors (especially Bi-Sr-Ca-Cu-O) are cooled in a very small magnetic field. For ease of interpretation the experiments relate exclusively to Bi-Sr-Ca-Cu-O in finely powdered form. Attention is paid not only to the magnetic moment observed during a field cool, but also to the moment remaining during a subsequent zero-field warm and to the moment developed during a field warm following a zero-field cool. The moments observed during a field cool are similar to those reported by other authors. A tentative interpretation of the results is made in terms of a model in which there is a concentration within the material of small local moments that can be polarized during a field cool. Information about both the magnitudes of these local moments and their concentrations is deduced. Evidence is presented that the observed local moments are too small to be accounted for by half flux quanta trapped in loops or within grains, such half flux quanta being associated with π junctions or d-wave pairing. This suggests that either the local moments originate in some other way or the model is incorrect. © 1996 The American Physical Society.

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