Scaling of the Equilibrium Magnetization in the Mixed State of Type-II Superconductors

TL;DR

This paper presents a scaling method for analyzing mixed-state magnetization data in type-II superconductors, enabling accurate assessment of the temperature dependence of the upper critical field and providing insights into the nature of the phase transition in high-temperature superconductors.

Contribution

It introduces a universal scaling procedure for magnetization data that does not require absolute H_c2(T) values, aiding validation of theoretical models and understanding of phase transitions.

Findings

The scaling procedure accurately captures the temperature variation of H_c2(T).

Magnetization shifts at the transition can vary in sign, challenging the vortex lattice melting interpretation.

The method offers a new way to analyze equilibrium magnetization data in superconductors.

Abstract

We discuss the analysis of mixed-state magnetization data of type-II superconductors using a recently developed scaling procedure. It is based on the fact that, if the Ginzburg-Landau parameter kappa does not depend on temperature, the magnetic susceptibility is a universal function of H/H_c2(T), leading to a simple relation between magnetizations at different temperatures. Although this scaling procedure does not provide absolute values of the upper critical fieldH_c2(T), its temperature variation can be established rather accurately. This provides an opportunity to validate theoretical models that are usually employed for the evaluation of H_c2(T) from equilibrium magnetization data. In the second part of the paper we apply this scaling procedure for a discussion of the notorious first order phase transition in the mixed state of high temperature superconductors. Our analysis, based on experimental magnetization data available in the literature, shows that the shift of the magnetization accross the transition may adopt either sign, depending on the particular chosen sample. We argue that this observation is inconsistent with the interpretation that this transition always represents the melting transition of the vortex lattice.