Change of strength of vortex pinning in YBCO due to BaZrO_3 inclusions

TL;DR

This study investigates how BaZrO3 inclusions affect vortex pinning in YBCO superconducting films at microwave frequencies, revealing enhanced pinning and suppressed thermal activation due to the inclusions.

Contribution

It provides new insights into the impact of BaZrO3 inclusions on vortex pinning properties in YBCO at high frequencies, highlighting changes in microwave resistivity and pinning dynamics.

Findings

BaZrO3 inclusions reduce field-induced microwave resistivity increase.

Inclusions suppress thermal activation effects.

Enhanced and field-independent pinning observed with BaZrO3.

Abstract

We probe the short-range pinning properties with the application of microwave currents at very high driving frequencies (47.7 GHz) on YBa$_2$Cu$_3$O$_{7-\delta}$ films with and without sub-micrometer BaZrO$_3$ inclusions. We explore the temperature and field ranges 60 K$<T<T_c$ and 0$<\mu_0H<$0.8 T, with the field applied along the c-axis. The magnetic field induces a much smaller increase of the microwave resistivity, $\Delta \rho_1(H)+\mathrm{i}\Delta \rho_2(H)$, in YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$ with respect to pure YBa$_2$Cu$_3$O$_{7-\delta}$. $\Delta \rho_1(H)$ is slightly superlinear in pure YBa$_2$Cu$_3$O$_{7-\delta}$ (suggesting a possible contribution of thermal activation), but linear or sublinear in YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$ (suggesting a possible suppression of thermal activation as a consequence of BaZrO$_3$ inclusions). These features persist up to close to $T_c$. We discuss our data in terms of the ratio $r=\Delta X_s'(H)/\Delta R_s'(H)$ in the framework of the models for the microwave surface impedance in the mixed state. Large $r$ are found in YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$, with little field dependence. By contrast, smaller values and stronger field dependences are found in pure YBa$_2$Cu$_3$O$_{7-\delta}$. We discuss the different field dependence of the pinning constant.