Abstract

Temperature dependences of the microwave surface impedance, Zs(T), are measured in the c-axis oriented single-crystal high-Tc superconducting cuprate YBa2Cu3O7−δ (YBCO) thin films deposited by the off-axis dc magnetron sputtering onto CeO2-buffered single-crystal sapphire substrates (film thickness is d≈150, 300, 480nm). Measurements are performed by a use of the coplanar resonator as well as the end-plate cylindrical cavity resonator techniques at several discrete frequencies within the range 5–134GHz. The measurements have revealed unexpected peculiarities on the Zs(T)-dependences for the most perfect films under study. The peculiarities appear to be most strongly pronounced on the temperature dependences of the film surface resistance Rs(T)=Re{Zs(T)}. The most important features of the unusual surface resistance behavior are: (i) the temperature dependence Rs(T) of the YBCO films under study at low temperatures obeys the exponential law: Rs(T)=Rres+R0exp[−Δs∕T] with a small energy gap Δs(Δs≈0.5Tc at f=5GHz); (ii) the most perfect films reveal a distinct two-peak structure of the Rs(T) dependence with peaks positioned at 27–30K and 48–51K, while such peaks are not observed in less perfect films. The peaks are mostly pronounced at moderate (e.g., 34GHz) frequencies and gradually disappear both at higher and lower frequencies, while their temperature positions remain unchanged. These features of perfect single-crystalline YBCO films are believed to reveal their intrinsic electron properties. Taking into account the possibility of a mixed (s+id)-type pairing symmetry as well as a significant role of extended out-of-plane crystal defects (such as dislocation lines or twin planes) in Bogolyubov’s quasiparticle scattering within the most perfect YBCO films, one can suggest a consistent explanation for the anomalies observed in the Zs(T) behavior.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.