Improvement of microwave characteristics for high-T _c superconductor (YBCO) films by ion irradiation treatment

Abstract Measurements of the microwave surface impedance for high-temperature superconductor YBa 2 Cu 3 O 7− x (YBCO) films irradiated by 3 MeV Au 2+ ions at three irradiation doses (10 10 cm −2 , 10 11 cm −2 , and 10 12 cm −2 ) were carried out at different temperatures (below the critical temperature of T с ≈ 90 К) and various rf current amplitudes by the use of the microstrip resonator technique. A noticeable decrease in the surface resistance and an enhancement of the linear response range at low temperatures were observed for moderately irradiated film exposed to an irradiation dose of 10 11 cm −2 , while at higher irradiation doses (10 12 cm −2 ) an increase in the surface resistance and a decrease in the linear response range were observed for all temperatures below T c . These results are discussed in the framework of phenomenological theory for the microwave response of superconductors with nano-sized structural defects.