Tl2Ba2CaCu2O8 films with very low microwave surface resistance up to 95 K

Abstract

Very low surface resistance Tl₂Ba₂CaCu₂O₈ films of thickness 1.0 μm on (100) LaAlO₃ were fabricated and characterized. The films are highly c‐axis oriented (x‐ray diffraction rocking curve full width half maximum of 0.68°) with good in‐plane epitaxy with respect to the substrate. The T_c of the films was 107.6±0.5 K as measured by ac magnetic susceptibility. The surface resistance at 10 GHz was measured with the parallel plate resonator technique and found to be 23±5 μΩ at 4.2 K, 130±20 μΩ at 77 K, and 300±60 μΩ at 95 K. Using a 20 GHz TE₀₁₁ end‐wall replacement copper cavity, the surface resistance was found to be comparable to that of copper, about 18 mΩ, at 104±1 K. The surface resistance of the films is significantly lower than that of all films reported to date at temperatures above 70 K and only slightly higher than the best high‐temperature superconductor films reported to date at 4.2 K.