Growth and property analysis of large-area epitaxial Tl-2212 high temperature superconducting films

摘要

The extensive use of large-area high temperature superconducting (HTS) thin films has emerged in superconducting microwave devices. The interest in Tl-based HTS films arises from their high critical temperature (T-c), allowing the microwave device made on Tl films to work above the liquid nitrogen temperature zone. Here, we introduce a simplified two-step method to fabricate high-quality Tl2Ba2CaCu2O8 (Tl-2212) films on 2-inch LaAlO3 substrates. This method enables the preparation of Tl-2212 films to be easy and repeatable, promoting the theoretical research and practical applications of Tl-based films. Based on the high reproducibility of this fabricating process, we studied the superconducting properties of T-c, the critical current density J(c) (77 K, zero field) and surface resistance (R-s) of 2-inch Tl-2212 films. Results show that the T-c values of the sample films prepared at different conditions vary from 99 K to 103 K, depending on the oxygen content; the J(c) of the films ranges from 0.7 to 1.8 MA/cm(2), relying on the surface roughness. On the basis of the two-fluid model, the influence of J(c) on R-s of the Tl-2212 films is incorporated to explain the variation of R-s in different samples.