Critical Currents and Order-Disorder Phase Transition in the Vortex States of YBa2Cu4O8 with Chemically Introduced Disorder
arXiv:cond-mat/0107452 · doi:10.1103/PhysRevB.65.094518
Abstract
A series of YBa_{2-x}Sr_xCu_4O_8 single crystals was measured to study the influence of site disorder on the transition line Hss(T) between quasi-ordered vortex lattice and highly disordered vortex glass, as well as on the maximum critical current density within the glass phase, jcmax. When 32% of Ba is replaced by Sr, jcmax is an order of magnitude higher than in the unsubstituted compound. In contrast, the transition field Hss first drops by a factor of about five with a substitution of just 10% of Sr for Ba, and then remains approximately constant for higher Sr contents. Our results indicate that in very clean systems the order-disorder transition is affected very strongly by any crystallographic disorder, while above a certain threshold it is relatively robust with respect to additional disorder. In all substituted crystals Hss monotonically decreases with an increase of temperature.
arXiv commentText revised, some figures replaced, 11 pages, 10 figures, to appear in PRB
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