Reversible magnetization, critical fields, and vortex structure in grain-alignedYBa2Cu4

Abstract

Reversible-magnetization data have been studied for YBa2Cu408 in order to determine the thermodynamic properties and the magnetic-field dependence of the superQuid density. By fitting the Hao-Clem variational model to the reversible magnetization data below T, superconducting parameters such as the Ginzburg-I andau parameter e, the thermodynamic critical field H, and the superconducting order parameter are determined. The upper and lower critical fields H 2, 0 i, the penetration depth A, and the coherence length f are derived. Within the model there is a direct connection between the magnetization and the superBuid density, so the vortex structure, the behavior of the average order parameter in (H, T) plane, and the magnetic-field dependence of the super8uid density are obtained. In the high-field region, the evidence of strong vortex Quctuation effects is observed and explained by vortex Huctuation for a three-dimensional superconductor. The mean-field transition temperature T (H) and dH 2, /dT near T, derived from the analysis of vortex Huctuation effects are comparable with fitting results.

Ginzburg-Landau theory of type II superconductors in magnetic field

“…For example in optimally doped Y BCO superconductor one can establish the LLL scaling for fields above 3T and temperature above 70K (see, for example, (Sok et al, 1995)). A glance at the data however shows that above T c the scaling is generally unconvincing: the LLL magnetization is much larger that the experimental one above T c .…”

Three-dimensional superconducting behavior and thermodynamic parameters ofHgBa2Ca0.86Kim1, Lee2, Sui3 et al. 1996Phys. Rev. B302170View full textAdd to dashboardCite

“…3͒ and YBa 2 Cu 4 O 8 ͑Y-124͒. 4 But, in these superconductors, the vortex fluctuation effect is not well investigated quantitatively. This should be studied in detail.…”

Melting of the vortex lattice in high−Tcsuperconductors

“…Experimentally it is often claimed that one can establish the LLL scaling for fields above 3 T (see, for example, ref. [32]). …”