On extrinsic effects in the surface impedance of cuprate superconductors by weak links

摘要: The reported rf surface impedance of superconducting cuprates continues to drop with 2 years improving material quality. As leading indicator for quality the weak‐link critical current jcJ(T≊ 0, B ≊ 0) has grown from 102 106 A/cm2 and thus Josephson penetration depth λJ ∝ 1/√jcJ excess normal (leakage) tunnel jbl are shrinking. This jcJ growth now saturated, whereas residual Zres is still shrinking improvements. shows clearly that an extrinsic property. Evidence due large leakage small weak links, where latter destroys intrinsic shielding a λI thin‐seam deep into bulk, presented. causes losses Rres (ωμ0)2λJ3σbl/2. stays finite at T ≂ 0 by σbl(T → σbl (∝jbl) being amplified (λJ/λI)3 ≳ 103 as weighting factor. With slow crystal links improved their density reduced so values better than RNb(4....