Critical currents and order-disorder phase transition in the vortex states of YBa2Cu4O8 with chemically introduced disorder -: art. no. 094518

A series of YBa2-xSrCu4O8 single crystals was measured to study the influence of site disorder on the transition line H-ss(T) between quasiordered vortex lattice and highly disordered vortex glass, as well as on the maximum critical current density within the glass phase, j(c)(max). When 32% of Ba is replaced by Sr, j(c)(max) is an order of magnitude higher than in the unsubstituted compound. In contrast, the transition field H-ss first drops by a factor of about 5 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 H-ss decreases monotonically with an increase of temperature.