Two types of Hc2(T) dependences in Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+delta) with different Yttrium content

TL;DR

This study reanalyzes magnetization data of Bi-2212 superconductors with varying yttrium content, revealing two distinct types of Hc2(T) dependencies and challenging previous interpretations based on inadequate analysis methods.

Contribution

The paper introduces a new analysis approach that corrects prior misinterpretations of Hc2(T) in Bi-2212, showing different doping levels lead to qualitatively different Hc2(T) behaviors.

Findings

Normalized Hc2(T) curves differ from previous results.

Hc2(T) dependencies do not follow Werthamer-Helfand-Hohenberg theory.

Two samples exhibit qualitatively different Hc2(T) behaviors.

Abstract

We reanalyze the magnetization data collected on Bi_2Sr_2Ca_(1-x)Y_xCu_2O_(8+y) samples (Kim at al, Phys. Rev. B 72, 64525 (2005)) and argue that the method, which was used for the analysis of equilibrium magnetization data, is not adequate to the experimental situation. As a result, the temperature dependencies of the upper critical field Hc2(T) and the magnetic field penetration depth lambda (T), obtained in this work, are misinterpreted. Using a different approach to analysis, we demonstrate that the normalizedHc2(T) curves are rather different from those presented in the original publication and do not follow predictions of the Werthamer-Helfand-Hohenberg theory. Another important observation is that the Hc2(T) dependencies for two samples with different levels of doping are qualitatively different.