Resistive upper critical fields and irreversibility lines of optimally-doped high-T_c cuprates

TL;DR

This study measures the resistive upper critical fields and irreversibility lines in various high-T_c cuprates under high magnetic fields, revealing their dependence on anisotropy and the absence of low-temperature saturation.

Contribution

It provides detailed resistive measurements of critical fields in high-T_c cuprates, highlighting the influence of anisotropy on their magnetic properties and behavior at low temperatures.

Findings

H_{c2} and H_{irr} depend monotonically on anisotropy.

No saturation of H^{ ho}(T) observed at low temperatures.

Materials with larger anisotropy show stronger positive curvature.

Abstract

We present the resistively-determined upper critical field H^{\rho}_{c2}(T) and the irreversibility lines H^{\rho}_{irr}(T) of various high-T_c cuprates, deduced from measurements in 61-T pulsed magnetic fields applied parallel to the c-axis. The SHAPE of both H^{\rho}_{c2}(T) and H^{\rho}_{irr}(T) depends monotonically on the anisotropy of the material and none of the samples show saturation of H^{\rho}(T) at low temperatures. The anomalous positive curvature, d^2 H^{\rho}/dT^2 > 0, is the strongest in materials with the largest normal-state anisotropy, regardless of whether anisotropy is varied by changing the carrier concentration or by comparing a variety of optimally-doped compounds.