Directional vortex pinning at microwave frequency in YBa\(_{2}\)Cu\(_3\)O\(_{7-x}\) thin films with BaZrO\(_3\) nanorods

Abstract

We investigate the effect of the anisotropy and of the directional pinning in YBa\(_2\)Cu\(_3\)O\(_{7-x}\) films grown by pulsed laser ablation from targets containing BaZrO\(_3\) at 5% mol. BaZrO\(_3\) inclusions self-assemble to give nanorods oriented along the c-axis, thus giving a preferential direction for vortex pinning. The directionality of vortex response is studied at high ac frequency with the complex microwave response at 48 GHz, as a function of the applied field and of the angle \(\theta\) between the field and the c-axis. The complex microwave response does not exhibit any angular scaling, suggesting that the structural anisotropy of YBa\(_2\)Cu\(_3\)O\(_{7-x}\) is supplemented by at least another preferred orientation. The pinning parameter \(r\) shows evidence of directional pinning, effective in a wide range of angles around the c-axis (thus ascribed to BZO nanocolumns).