Proton radiation effects in microwave cavities and ring resonators fabricated from YBa2Cu3O7−δ

Abstract

We report the first radiation effects study on a superconducting ring resonator made from thin‐film YBa₂Cu₃O_7−δ. Exposure to 2 MeV protons causes the superconducting transition temperature T_c to decrease predictably with fluence. For temperatures below about 0.9T_c , there is no significant change in the transmission coefficient, the center frequency, or the quality factor Q of the resonator, even for doses in excess of 4×10¹⁶ protons/cm² (∼0.04 displacements per film atom). Similarly, the low‐temperature surface resistance R_s of an unpatterned film does not change with irradiation. We show that this insensitivity to radiation is not predicted by standard theory, and that the dominant part of R_s at low temperature is the residual resistance R₀. Thus any viable theory describing the origin of R₀ must, as a criterion, explain the origin of its insensitivity to large irradiation doses. This criterion is used to evaluate theories ascribing R₀ to weak links, flux pinning, impurities, and lattice imperfections.