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.

Local vortex dynamics in BizSrzCaCu208 single crystals was studied using novel microscopic GaAs/AlGaAs Hall-sensor arrays. The irreversibility line (IL) is found to exist in the absence of bulk pinning. At high temperatures the IL is due to geometrical barriers whereas at intermediate temperatures the irreversible behavior is determined by surface barriers. Bulk pinning governs the IL only at T e 22 K.

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.

In this work we analyze the influence of random point defects introduced by 3 MeV proton irradiation on the critical current density (J c ) and vortex dynamics of a Ba(Fe 0.925 Co 0.075 ) 2 As 2 single crystal. The results show that at low temperatures (T ) the irradiation produces an enhancement of J c of up to 2.6 times. However the J c (T ) retention at different magnetic fields (H ) in the elastic regime, estimated by the n exponent in J c vs (1 − (T /T c ) 2 ) n , is poorer after the irradiations due to the thermal softening of the pinning by the random point defects. We found that the elastic-to-plastic crossover and melting lines are only affected by the reduction of the superconducting critical temperature (T c ); they are exactly the same after rescaling the phase diagram by T /T c . The pinning mechanisms in the single crystals can be associated with a mixed pinning landscape that produces a modulation in S(H , T ) as a consequence of a fishtail or second peak in the magnetization.

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