# Entropy jump at the first-order vortex phase transition in Bi2Sr2CaCu2O8+{\delta} with columnar defects

## TL;DR

This study investigates the entropy change at the vortex melting transition in Bi2Sr2CaCu2O8+{eta} crystals with columnar defects, revealing how disorder affects the transition and comparing experimental results with theoretical models.

## Contribution

It provides the first detailed measurement of entropy jumps at the vortex transition in crystals with columnar defects and compares these with theoretical predictions.

## Key findings

- Entropy jump decreases with increased columnar defect density.
- Pristine samples follow electromagnetic coupling theory, while defected samples deviate.
- Disorder influences the vortex melting transition behavior.

## Abstract

We study the entropy jump associated with the first-order vortex melting transition (FOT) in Bi2Sr2CaCu2O8+{\delta} crystals by means of Hall probe magnetometry. The samples present a diluted distribution of columnar defects (CD) introduced by irradiation with Xe ions. The FOT is detected in ac transmittivity measurements as a paramagnetic peak, the height of which is proportional to the enthalpy difference entailed by the transition. By applying the Clausius-Clapeyron relation, we quantify the evolution of the entropy jump {\Delta}s as a function of the FOT temperature, TFOT, in both pristine crystals and crystals with CD. On increasing the density of CD, {\Delta}s decreases monotonically with respect to values found in pristine samples. The {\Delta}s versus TFOT dependence in the case of pristine samples follows reasonably well the theoretical prediction of dominant electromagnetic coupling for a model neglecting the effect of disorder. The data for samples with a diluted distribution of CD are not properly described by such a theoretical model.

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Source: https://tomesphere.com/paper/1903.11150