ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
