Epitaxial Tl2CaBa2Cu2O8 thin films with low 9.6 GHz surface resistance at high power and above 77 K

We report measurements of the dc and microwave properties of epitaxial thin films of Tl2CaBa2Cu2O8 on LaAlO3. ac magnetic susceptibility measurements yield critical temperatures at the transition midpoint Tc∼100 K and 10–90% transition widths of ∼1.0 K. We observed a critical current density of 1.06×106 A/cm2 at 77 K measured by dc transport. We measured a low-power surface resistance of Rs=0.2 mΩ at 9.55 GHz and 77 K. This is ∼50 times lower than oxygen-free high-conductivity (OFHC) Cu at the same frequency and temperature. At 90 K, RS rises to 0.4 mΩ, and at 95 K, RS=0.7 mΩ. We measured the microwave power dependence of RS at 77, 90, and 95 K. At high microwave field (≳30 G, 77 K) Rs=0.8 mΩ, more than ten times lower than OFHC Cu.