Strong Reduction of the Field-Dependent Microwave Surface Resistance in YBCO with BaZrO_3 Inclusions

TL;DR

This study demonstrates that incorporating BaZrO₃ inclusions into YBCO films significantly reduces the magnetic field-dependent microwave surface resistance, indicating enhanced vortex pinning and potential for improved superconducting microwave applications.

Contribution

The paper reports the first detailed investigation of BaZrO₃ inclusions in YBCO films showing a strong reduction in field-dependent microwave surface resistance due to steep vortex pinning potentials.

Findings

BaZrO₃ inclusions cause a significant decrease in surface resistance under magnetic fields.

YBCO films with BaZrO₃ exhibit steeper vortex pinning potentials.

Enhanced microwave performance in YBCO with BaZrO₃ inclusions.

Abstract

We present measurements of the magnetic field dependent microwave surface resistance in laser-ablated YBa$_2$Cu$_3$O$_{7-\delta}$ films on SrTiO$_3$ substrates. BaZrO$_3$ crystallites were included in the films using composite targets containing BaZrO$_3$ inclusions with mean grain size smaller than 1 $\mu$m. X-ray diffraction showed single epitaxial relationship between BaZrO$_3$ and YBa$_2$Cu$_3$O$_{7-\delta}$. The effective surface resistance was measured at 47.7 GHz for 60$< T <$90 K and 0$< \mu_0H <$0.8 T. The magnetic field had a very different effect on pristine YBa$_2$Cu$_3$O$_{7-\delta}$ and YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$, while for $\mu_0H=$0 only a reduction of $T_c$ in the YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$ film was observed, consistent with dc measurements. At low enough $T$, in moderate fields YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$ exhibited an intrinsic thin film resistance lower than the pure film. The results clearly indicate that BaZrO$_3$ inclusions determine a strong reduction of the field-dependent surface resistance. From the analysis of the data in the framework of simple models for the microwave surface impedance in the mixed state we argue that BaZrO$_3$ inclusions determine very steep pinning potentials.