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Critical current densities (Jc) and irreversibility fields (Birr) of high-Tc superconductors AuBa2Can−1CunO2n+3 [Au-12(n−1)n, n=3,4] prepared under high pressure were determined from the hysteresis in DC magnetization loop. Both the Jc and Birr values of the Au-1234 phase were larger than those of Hg- and Bi-based cupurate superconductors, but smaller than those of the Y-123 superconductor. This result suggests that the electronic structure of Au-1234 is less anisotropic compared with the Hg- and Bi-phases. The Au-1223 phase showed very small Jc values corresponding to its small superconducting volume fraction. [Copyright &y& Elsevier]

Results of X-ray fluorescence measurements of MA[sub 2]Ca[sub n-1]Cu[sub n]O[sub 2n+3] compounds with [M-12(n 1)n] type structures, (C[sub 0.8]N[sub 0.2]Sr[sub 2]CuO[sub 5.3], [Cu[sub 0.25](C,N)[sub 0.75]]Sr[sub 2]CaCu[sub 2]O[sub y], Cu[sub 0.5]V[sub 0.5]Sr[sub 2]CaCu[sub 2]O[sub 7.5], Cu[sub 0.5]V[sub 0.5]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub 9.4], Cu[sub 0.5]V[sub 0.5]Sr[sub 2](Ca[sub 3.6]Sr[sub 0.4])Cu[sub 5]O[sub 13.5] and Cu[sub 0.5]V[sub 0.5]Sr[sub 2](Ca[sub 4.7]Sr[sub 0.3])Cu[sub 6]O[sub 15.3]), are presented. The experiments show that C-atoms form a distorted CO[sub 3] oxyacid group with a partial substitution of copper and nitrogen atoms in the M-sites. We conclude that the CO[sub 3, sup 2-] group in (C,N) Sr[sub 2]Ca[sub n-1]Cu[sub n]O[sub y] and (Cu,C,N) Sr[sub 2]Ca[sub n-1]Cu[sub n]O[sub y] is substituted by the NO[sub 2, sup -] which induces the creation of the hole carriers in these compounds. We have found that V-atoms in the given compounds form (VO[sub 4])[sup 3-] tetrahedrons and have a pentavalent state. [ABSTRACT FROM AUTHOR]

Abstract: We have studied the electronic structure near the Fermi level of the layered cobaltate superconductor Na0.35CoO2·1.3H2O using laser-excited ultrahigh-resolution photoemission spectroscopy (PES). In the normal state, we observed the formation of a pseudogap with an energy scale of ∼20meV. Across the superconducting transition, we observed the leading-edge shift at 3.5K compared to that at 10K, indicating superconducting gap (SC gap) opening having a gap value Δ of 0.5–0.7meV. The energy scale of the SC gap is ∼20 times smaller than that of the pseudogap, suggesting the existence of competing order parameters at low temperatures. [Copyright &y& Elsevier]