Temperature dependence of the penetration depth and effective dielectric constant measured by YBa₂Cu₃O_7-δ microstrip ring resonators

YBa₂Cu₃O_7-δ(YBCO) superconducting ring resonators with a YBCO ground plane were successfully fabricated using double-side YBCO films deposited on LaAlO₃ (LAO) substrates. The temperature dependent London penetration depth, Δλ = λ(T)-λ(5 K), was systematically studied by varying the oxygen content of the same resonator structure. For fully oxygenated case (δ = 0.05), the resonator exhibits a quality factor Q>10⁴ at 16 K, and Δλ(T) displays a linear behavior over a wide range of temperatures. With increasing δ (e.g. δ = 0.2, 0.4), although Δλ is still linear in temperature, the slope changes with increasing oxygen deficiency. The results suggest that, in the underdoped regime, the inelastic scattering of charged carriers may become increasingly prominent. From the effective dielectric constant obtained from the ring resonator the dielectric constant of the LAO substrate was estimated to be ε_r≅25.5 at 5 K and a frequency of about 3.6 GHz.