Experimental evidence of the dominant role of low-angle grain boundaries for the critical current density in epitaxially grown YBa_2Cu_3O_(7-δ) thin films

摘要

Thin films of the high-temperature superconductor YBa_2Cu_3O_(7-δ) (YBCO) show an increase of the critical current density if grown on nanostructured SrTiO_3 (STO) substrate. The temperature dependence of the critical current density of such a film was measured and compared to j_c(T) grown on regular [100] STO. The magneto-optical imaging technique was used to measure the flux-density distribution in the film and by applying an inversion scheme of the law of Biot and Savart the current density distribution in the film was calculated with a spatial resolution of 5 μm. By comparing the results with theoretical models for the temperature dependence of j_c in conventional HTSC thin films, a possible explanation for the increase of the critical current density due to the nanostructuring is presented. In addition, a complete scenario is obtained of the pinning mechanisms in YBCO thin films epitaxially grown on STO for the investigated temperature range of T=8-70 K from the results.