Upper critical field, fluctuation conductivity, and dimensionality ofYBa2Cu3

Abstract

The upper critical Seld H, q and fiuctuation conductivity were measured for highly oriented thin nlHls of YBa2Cu307 -. The H, 2 results demonstrate the intrinsic anisotropy in this layered su-

Magnetoresistivity of thin YBa2Cu3O7−δ films on sapphire substrate

“…The obtained results are in agreement with earlier reported data [9] and our expectations since we consider temperatures very close to T c where ξ becomes large and therefore the twodimensional approximation d << ξ [11] is justified.…”

“…Similar B c2 (T) behavior has been demonstrated by Yeshurun [13] and Tinkham [14] with an exponent of n = 1.5 for 100 µm YBCO crystals. Also Oh et al [9] reported an upturn curvature with n = 1.3 for 1 µm thick epitaxial YBCO films using both a 0.9R n criterion and the critical fluctuation theory. The thickest studied YBCO film in this report with d = 100 nm shows a B c2 (T) dependence with the exponent n = 1.14.…”

“…The definition of the critical temperature T c has a major influence on B c2 (T) for the high-temperature superconductor YBCO as it was already mentioned by Oh et al [9]. Therefore, to find the correct transition temperature the fluctuation conductivity theory of Aslamazov and Larkin (AL) [10] …”

Unscaling Superconducting Parameters with Tc for Bi-2212 and Bi-2223: A Magnetotransport Study in the Superconductive Fluctuation Regime

“…The difference might be attributable to the difference in the measurement method or in the sample forms (single crystals vs. aligned powders). The good fitting results produced without the use of a C factor, 22) as well as the agreement between the obtained superconducting parameter and the literature values, indicate that the obtained parameters are reasonable.…”

“…First, the zero-field, ρ ab , data was analyzed using the formula, ρ ab = 1/(ρ −1 n + σ 2D−AL ), where ρ n is the in-plane resistivity when superconductive fluctuation effects are absent and σ 2D−AL is the zero-field two-dimensional (2D) Aslamazov-Larkin (AL) form 21) In this study, ρ n is simply assumed to be ρ n = aT + b. We did not use a C factor (i.e., C = 1), 22) which is defined by the ratio of the actual ρ ab of an imperfect crystal to an ideal crystal and, thus, it phenomenologically adjusts the magnitude of the fluctuation conductivity (σ 2D−AL → σ 2D−AL /C). We optimized T c0 and ρ n to reproduce the zero-field data.…”