On the low-temperature microwave response of a YBa2Cu3O7−σ epitaxial film determined by a new measurement technique

Abstract

The temperature dependence of the surface resistance RS(T) of a high-quality 600-nm thick YBa2Cu2O7−σ epitaxial film, deposited on a MgO single-crystal substrate, has been investigated. The measurements were performed in the temperature range from Tc to 2K using a new technique—the application of a sapphire hemispherical resonator with whispering gallery mode in the 8-mm wavelength range (Ka band). The new measurement technique makes it possible to reach high measurement sensitivity for RS(T) (to 10μΩ) at low temperatures. A linear dependence of RS(T) was obtained in the range 2–15K, in agreement with d-wave symmetry of the order parameter. The value found in the present work for the residual resistance Rres=RS(T→0) shows that the microwave properties of the film are close to those of single-crystals and, apparently, the internal properties of the superconductor determine Rres. Analysis of the published data shows that Rres(ω)∼ω3∕2 for YBa2Cu3O7−σ single crystals and films, and the nature of the residual microwave resistance remains unknown.