3D Lowest Landau Level Theory Applied to YBCO Magnetization and Specific Heat Data: Implications for the Critical Behavior in the H-T Plane

TL;DR

This paper applies a 3D lowest Landau level theory to analyze magnetization and specific heat data of YBCO high-temperature superconductors, questioning the significance of 3DXY scaling and flux lattice melting evidence.

Contribution

It demonstrates the limitations of 3D LLL functions in describing YBCO data and challenges previous interpretations of flux lattice melting and 3DXY scaling relevance.

Findings

3D LLL functions are less successful for YBCO than for more anisotropic HTSCs.

3DXY scaling does not fit the specific heat data in the critical region.

Alternative explanations for flux lattice melting evidence are proposed.

Abstract

We study the applicability of magnetization and specific heat equations derived from a lowest-Landau-level (LLL) calculation, to the high-temperature superconducting (HTSC) materials of the YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) family. We find that significant information about these materials can be obtained from this analysis, even though the three-dimensional LLL functions are not quite as successful in describing them as the corresponding two-dimensional functions are in describing data for the more anisotropic HTSC Bi- and Tl-based materials. The results discussed include scaling fits, an alternative explanation for data claimed as evidence for a second order flux lattice melting transition, and reasons why 3DXY scaling may have less significance than previously believed. We also demonstrate how 3DXY scaling does not describe the specific heat data of YBCO samples in the critical region. Throughout the paper, the importance of checking the actual scaling functions, not merely scaling behavior, is stressed.