TEMPERATURE-DEPENDENCE OF THE MEISSNER PENETRATION LENGTH IN SUBMICRON VORTEX-FREE AND VORTEX-TRAPPED Y-BA-CU-O PARTICLES - TEST FOR APPLICABILITY OF THE MODIFIED LONDON EQUATION

To test the applicability of the modified London equation (MLE) the me thod based on comparison of the temperature dependencies of the penetr ation length lambda(ab) in the Meissner and the vortex states is propo sed. For experimental testing we investigate the magnetic properties o f submicron superconducting Y-Ba-Cu-O particles prepared by a citrate gel modification of the sol-gel technique. It is found that the depend ence lambda(ab)(2)(0)/lambda(ab)(2)(T) obeys a power law with the expo nent n = 2.0 +/- 0.2 and n = 2.5 +/- 0.05 in the Meissner and the vort ex states, respectively. This difference indicates that MLE is not val id in the vortex state at least in the scale of the used particles i.e . of some hundred Angstrom. Possible reasons for this are discussed. ( C) 1997 Elsevier Science B.V.