Critical current density and ac harmonic voltage generation in $YBa_2Cu_3O_{7-\delta}$ thin films by the screening technique

TL;DR

This study investigates the temperature and magnetic field effects on harmonic voltage generation in YBa2Cu3O7−δ superconducting thin films using the screening technique, revealing insights into flux dynamics and critical current density behavior.

Contribution

It applies the Sun model and empirical laws to analyze harmonic generation, providing a comprehensive understanding of flux processes in superconducting thin films.

Findings

Most models fit the fundamental voltage well

Higher harmonics are poorly reproduced by existing models

Higher harmonics reveal complex flux dynamics like creep and thermally assisted flow

Abstract

The temperature and field dependence of harmonics in voltage $V_n=V'_n-iV"_n$ using the screening technique have been measured for $\mathrm{Y}\mathrm{Ba}_{2}\mathrm{Cu}_3\mathrm{O}_{7-\delta}$ superconducting thin films. Using the Sun model we obtained the curves for the temperature-dependent critical current density $J_c(T)$. In addition, we applied the criterion proposed by Acosta et al. to compute $J_c(T)$. Also, we made used of the empirical law $J_c \propto (1-T/T_c)^n$ as an input in our calculations to reproduce experimental harmonic generation up to the fifth harmonic. We found that most models fit well the fundamental voltage but higher harmonics are poorly reproduced. Such behavior suggests the idea that higher harmonics contain information concerning complex processes like flux creep or thermally assisted flux flow.