Thermodynamics of the first-order vortex lattice melting transition in YBa$_2$Cu$_3$O$_{7-\delta}$

TL;DR

This paper models the vortex lattice melting transition in YBa₂Cu₃O₇−δ using the London approximation, accurately predicting the specific heat jump and magnetization changes observed experimentally, and confirms the anisotropic scaling behavior.

Contribution

It provides a refined theoretical calculation of the specific heat jump at the vortex melting transition, aligning with experimental data by properly accounting for temperature-dependent parameters.

Findings

Predicted specific heat jump matches experimental measurements.

Demonstrated consistency of magnetization slope changes at transition.

Validated anisotropic scaling theory with experimental angle measurements.

Abstract

Using the London approximation within the high field scaling regime, we calculate the jump in the specific heat $\Delta c$ at the first-order melting transition of the vortex lattice in YBa$_2$Cu$_3$O$_{7-\delta}$. This has recently been measured [A. Schilling et al., Phys. Rev. Lett. (78), 4833 (1997)] and reported to be at least 100 times higher than expected from the fluctuations of field induced vortices alone. We demonstrate how the correct treatment of the temperature dependence of the model parameters, which are singular at the mean-field $B_{c2}$ line, leads to good agreement between the predictions of the London model and the size of the experimental jump. In addition, we consider the changes in the slopes of the magnetization $\Delta(\partial M/\partial T)$ and $\Delta(\partial M/\partial H)$ at the transition. Using continuum anisotropic scaling theory we demonstrate the consistency of measurements at different angles of the magnetic field with respect to the crystal c-axis.