RESUMO
We report the first detailed and quantitative study of the Josephson coupling energy in the vortex liquid, Bragg glass, and vortex glass phases of Bi(2)Sr(2)CaCu(2)O(8+delta) by the Josephson plasma resonance. The measurements revealed distinct features in the T and H dependencies of the plasma frequency omega(pl) for each of these three vortex phases. When going across either the Bragg-to-vortex glass or the Bragg-to-liquid transition line, omega(pl) shows a dramatic change. We provide a quantitative discussion on the properties of these phase transitions, including the first order nature of the Bragg-to-vortex glass transition.
RESUMO
We report on a new type of correlated nanometer-scale pinning structure observed in a melt-processed (Nd0.33Eu0.38Gd0.28)Ba(2)Cu(3)O(y) (NEG-123). It consists of NEG/Ba-rich clusters in the stoichiometric NEG-123 matrix forming a lamellar array with a period of a few nanometers. These lamellas appear within regular twins, thus representing their fine substructure-sometimes straight, sometimes wavy. This new material structure correlates well with the significant enhancement of pinning at high fields, represented by irreversibility field above 14 T at 77 K (B parallel c). We believe that the new pinning medium enables one to significantly broaden the limits for high-field applications.
RESUMO
The low-field Bose-glass transition temperature in heavy-ion irradiated Bi(2)Sr(2)CaCu(2)O(8+delta) increases progressively with increasing density n(d) of irradiation-induced columnar defects, but saturates for n(d) greater or = 1.5 x 10(9) cm(-2). The maximum Bose-glass temperature corresponds to that above which diffusion of two-dimensional pancake vortices between vortex lines becomes possible, and the "linelike" character of vortices is lost. We develop a description of the Bose-glass line that quantitatively describes experiments on crystals with widely different track densities and material parameters.