Effect of Si-Ion Irradiation on Microwave Surface Resistance in YBa2Cu3Oy Thin Films in Magnetic Fields

In this study, we examined the effect of Si-ion irradiation on R
_s
of YBCO thin films. We measured R
_s
⁹⁰
and R
_s
⁰
of YBCO thin films in a magnetic field applied both normal and parallel to the film plane. Si-ion irradiation conditions were configured as follows: irradiation energy = 50–500 keV, irradiation ion density = 1–8 × 10
¹²
ion/ cm
²
. We found that the R
_s
⁹⁰
decreased through ion irradiation, and Si-ion irradiation with an irradiation energy of 200 keV and an irradiated ion density of 4 × 10
¹²
ion/cm
²
being the most effective configuration for reducing R
_s
⁹⁰
in high magnetic fields. Magnetic field-dependent R
_s
⁰
was quite small for all YBCO films with and without ion irradiation. When a magnetic field is applied parallel to the film plane, the blocking layers of the YBCO act as strong pins, therefore, R
_s
⁰
in the magnetic field is small without introduction of artificial pins. However, we found that the R
_s
⁰
of YBCO films became small with Si-ion irradiation than that of the YBCO film without Si-ion irradiation, that the condition of ion energy 200 keV and ion irradiation density 1 × 10
¹²
ion/cm
²
could reduce R
_s
⁰
most.