Torque Study of Layered Superconducting OxideBi₂Sr₂CaCu₂O_8+δSingle Crystal

Anomalous Reversible Torque in Layered Superconducting Bi2Sr2CaCu2OxSingle Crystal

“…The main fitting parameters obtained within modeling were ε = 78 and Ηc2 = 100 Τ. The obtained values seem to be reasonable and coincide with reported in [6]. Analogical value of the square root of the effective mass ratio ε was derived from measuring the longitudinal and transverse components of the equilibrium magnetization of crystals oriented at arbitrary angles with respect to the applied direction [16].…”

“…For calculations which give the best fit to the measured torque (Fig. 1) the following values of the decisive parameters were obtained: ' 0 = 0.5, α1 = 0.4, λ = 350 nm with ε = 78 and Ηc2 = 100 T (ε, Hc2 are reasonable and coincide with reported in [6,16]). In order to investigate the torque behaviour in layered quasi-2D superconduction we have performed several calculations of the torque using different values of ε = (m┴/m||) 1 / 2 , λ, αι, H and H c2.…”

“…As reasons for rather big discrepancies of the model parameters (ε, Η c2 ) reported in various papers [5][6][7]16], except imperfections of the investigated samples, it may be that flux-pinning under the field near the (α, b) plane is not neglected completely in real crystals of HΤC-superconductors. The performed calculations and comparison with experimental data prove that the layer discreteness can modify much torque behaviour observed in the strong anisotropic bismuth family superconductors.…”

“…The torque Τ as a function of angle 9H (the angle between applied field H and c-axis) shows sharp maximum near 90° and some cavity lightly below. The traditionally used phenomenology of Kogan's [2] seems to describe the behaviour of the torque in YBa2Cu3O x [3,4] well but not in higher anisotropic superconduction as Bi-and Tl-based compounds [6][7][8]. The above discrepancies are probably connected with 2D character of those superconducting materials.…”

“…The magnetic torque experiments have proved to be an extremely powerful technique to obtain the square root of the effective mass ratio according to the Kogan [2] model. The valueS obtained from these measurements for ε were ε ΠΙ 8 for YBa2 Cu3 Ox [3,4], ε 55-400 for Bi 2 Sr2 CaCu2Ox [5][6][7] and ε 94 for T12 Ba2 CaCu 2 Ox [8] respectively. Rather big discrepancies among the reported in literature results for parameter ε especially for Bi compounds suggest that Kogan's formula [2] based on the anisotropic Landau model is not applicable to the highly layered anisotropic superconducting materials.…”