Magnetization Measurements on Single Crystals of Superconducting Ba0.6K0.4BiO3

TL;DR

This study extensively measures the magnetization of Ba0.6K0.4BiO3 single crystals across a wide temperature and magnetic field range, revealing higher critical fields and unusual temperature dependencies that challenge existing theories.

Contribution

It provides new detailed magnetization data and critical field measurements, suggesting alternative interpretations of the superconducting transition in Ba0.6K0.4BiO3.

Findings

Higher T=0 critical fields than previously reported

Critical field temperature dependencies deviate from expected power laws

Temperature-dependent Ginzburg-Landau parameter

Abstract

Extensive measurements of the magnetization of superconducting single crystal samples of Ba0.6K0.4BiO3} have been made using SQUID and cantilever force magnetometry at temperatures ranging between 1.3 and 350 K and in magnetic fields from near zero to 27 T. Hysteresis curves of magnetization versus field allow a determination of the thermodynamic critical field, the reversibility field, and the upper critical field as a function of temperature. The lower critical field is measured seperately and the Ginzburg-Landau parameter is found to be temperature dependent. All critical fields have higher T = 0 limits than have been previously noted and none of the temperature dependence of the critical fields follow the expected power laws leading to possible alternate interpretation of the thermodynamic nature of the superconducting transition.