A study on the microwave responses of YBCO and TBCCO thin films by coplanar resonator technique

Abstract

YBa2Cu3O7(YBCO) thin films have been prepared by thermal coevaporation on LaAlO3(LAO) substrates, and Tl2Ba2CaCu2O8(TBCCO) thin films are synthesized by magnetron sputtering method on LAO substrates. The transition temperature Tc is90 K for YBCO/LAO and 104 K for TBCCO/LAO. Microwave responses of the films are studied systematically by coplanar resonator technique. Energy gaps of the films obtained are Δ0 = 1.04kBTc for YBCO films and Δ0 = 0.84kBTc for TBCCO films by analysing the temperature dependence of resonant frequencies of coplanar resonator. Penetration depth at 0 K λ0 = 198 nm for YBCO films and λ0 = 200 nm for TBCCO films could also be obtained by using the weak coupling theory and two fluid theory. Results of penetration depth and energy gap confirm the weak coupling properties of the films. In addition, microwave surface resistances Rs of YBCO/LAO and TBCCO/LAO are also investigated by analysing the quality factor and insert loss of the coplanar resonator. Surface resistance of TBCCO/LAO is less than that of YBCO/LAO, so that TBCCO/LAO films may have more potential applications.