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 method based on comparison of the temperature dependencies of the penetration length λab in the Meissner and the vortex states is proposed. For experimental testing we investigate the magnetic properties of submicron superconducting YBaCuO particles prepared by a citrate gel modification of the sol-gel technique. It is found that the dependence λab2(0)λab2(T) obeys a power law with the exponent n = 2.0 ± 0.2 and n = 2.5 ± 0.05 in the Meissner and the vortex states, respectively. This difference indicates that MLE is not valid in the vortex state at least in the scale of the used particles i.e. of some hundred A. Possible reasons for this are discussed.