Microwave Surface Resistance in 123 superconducting Thin Films

概要

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The microwave surface resistance, R_s, in various 123 superconducting thin films, in situ grown by pulsed laser deposition technique on different substrates was examined. Thermal annealing of MgO substrates prior to film deposition yields YBa_2Cu_3O_z (YBCO) films with low R_s value, ∿0.3 mΩ at 30 K, 22 GHz, which is close to the R_s value reported for best YBCO films which is attributed to the improved crystallinity of YBCO films. For Y_<0.98>Ca_<0.02>Ba_2Cu_3O_z films grown on MgO, we observed much suppressed R_s value (0.1 mΩ at 20 K, 22 GHz), which is three times smaller as compared to the R_s value of YBCO. It is presumed to be due to the enhanced J_c in this film caused by Ca doping. R_s(T) data of under-doped (both Co substituted YBCO as well as O_2 depleted YBCO films grown on LaAlO_3) films reveal that in general, under-doping leads to an enhancement in residual R_s values, which may be attributed to the increased penetration depth, λ, caused by the suppressed carrier content in the under-doped films. In the case of rare earth mixed (Dy<0.4>Ho<0.6>)Ba_2Cu_3O_z films grown on LaAlO_3, at 77 K and above, they exhibit a lower R_s value when compared to YBCO film. However, below 70 K, YBCO films showed a superior microwave properties.
社団法人電子情報通信学会の論文
2005-02-04