Upper critical field and anisotropy of the high-TcBi2

Abstract

The upper critical field (H, 2) of the 110-K Bi,Sr,Ca2Cu30 phase has been obtained using high-quality whiskers and the measurement of the field-induced resistive transition up to 7.5 T. In the presence of magnetic fields parallel and perpendicular to the c axis, linear relations are obtained in H, 2-T curves defined at the 50%%uo value of the extrapolated normal-state resistivity in the transition curves. According to the Werthamer-Helfand-Hohenberg theory and Ginzburg-Landau relations, the coherence lengths of 0 0 g,~( 0) = 29 A and g, (0)=0.93 A are obtained. The anisotropy ratio of the coherence length is 31.

Flux-Line-Lattice Melting and Upper Critical Field of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ Ceramic Samples

“…The electrical resistivity data are useful to construct an H c2 vs. T phase diagram for each sample [1,21]. The (H, T ) pairs were extracted from the 50% falls in the electrical resistivity curves at the superconducting transition (see Fig.…”

“…The influence of the grain misalignment on the H c2 (T ) boundary line is revealed by analyzing the values of the exponent α (see (1)). The latter was found to decrease from 3.7 ± 0.7 to 2.2 ± 0.2, indicating that α decreases appreciably with increasing compacting pressure, or more appropriately, with a better alignment of grains along the ab plane.…”

“…In the ρ(T , H ) data, the broadening of the superconducting transition in applied magnetic fields H > H c1 has been extensively investigated in several cuprates [1,3,4,[7][8][9][10][11][12][13][14]. There is a consensus that the width of the superconducting transition is strongly influenced by the anisotropy associated with the orientation of the applied magnetic field with respect to the CuO 2 planes [3,15,16].…”

“…The evaluation of the anisotropy of these lowdimensional materials can be inferred by measurements of their anisotropic quantities as the electrical resistivity, ρ, the upper critical field, H c2 , the critical current density, J c , etc. [1]. In addition, other features of these compounds as the large London penetration depth, high superconducting critical temperatures, and disorder conspire for strong fluctuations of the vortices that can lead to the melting of the vortex lattice.…”

“…The anisotropic behavior of high-T c materials have been frequently studied via H vs. T phase diagram, and the boundaries lines have been determined in single crystal specimens [1][2][3][4]. On the other hand, similar determinations, when using polycrystalline samples, would take into account several approximations arising from the complex granular nature of ceramic samples which contain voids, cracks, grain boundaries, and orientational disorder of the grains [5].…”