关于由晶体和粉末混合态中μ子自旋转动确定的YBa2Cu3O7 -δ、YBa2Cu4O8和La2-xSrxCuO4的超导能隙对称性
Concerning the superconducting gap symmetry in YBa2Cu3O7-δ, YBa2Cu4O8, and La2-xSrxCuO4 determined from muon spin rotation in mixed states of crystals and powders
摘要：
用μ子自旋旋转（μ+SR）方法测量了YBa_2Cu_3 O_7-δ（δ { \approx } 0.05）、YBa_2Cu_4 O_8和La_（2-x）Sr_xCuO_4（x ~ 0.15-0.17）超导混合态的局域磁场σ的平方根二阶矩，并对它们的超导能隙对称性进行了比较分析。对于取向晶体，它示出的σ对温度T和施加的场H的异常依赖性，作为测量和提取的a-和b-轴分量，归因于磁通钉扎和混乱，模糊了超导穿透深度的内在特征。来自定向晶体数据的随机平均值与相应的非定向粉末明显不同，这是由于高质量晶体中钉扎的影响较弱。钉扎扰动的相关指标，如σ的非单调H依赖性，不可重现的数据和表观转变温度的强H依赖性也是显而易见的。强的内禀钉扎抑制了σ的c轴分量的热异常，这反映了YBa 2Cu 3 O 7-δ和YBa 2Cu 4 O 8中的无节点能隙对称性。对于YBa 2Cu 3 O 7-δ，晶体（a-b分量，经脱钉校正）和粉末数据都反映了无节能隙（然而，对于晶体YBa 2Cu 4 O 8和La1.83Sr0.17CuO4，a-b对称性仍未解决）。讨论了晶体数据的多重能隙解释和节点能隙解释中所包含的信息，以及体μ+SR和表面灵敏测量之间观察到的差异。
英文摘要：
Muon spin rotation (μ+SR) measurements of square-root second moments of local magnetic fields σ in superconducting mixed states, as published for oriented crystals and powder samples of YBa2Cu3O7-δ (δ {\approx} 0.05), YBa2Cu4O8 and La2-xSrxCuO4 (x ~ 0.15-0.17), are subjected to comparative analysis for superconducting gap symmetry. For oriented crystals it is shown that anomalous dependences of σ on temperature T and applied field H, as-measured and extracted a- and b-axial components, are attributable to fluxon depinning and disorder that obscure the intrinsic character of the superconducting penetration depth. Random averages derived from oriented-crystal data differ markedly from corresponding non-oriented powders, owing to weaker influence of pinning in high-quality crystals. Related indicators for pinning perturbations such as non-monotonic H dependence of σ, irreproducible data and strong H dependence of apparent transition temperatures are also evident. Strong intrinsic pinning suppresses thermal anomalies in c-axis components of σ, which reflect nodeless gap symmetries in YBa2Cu3O7-δ and YBa2Cu4O8. For YBa2Cu3O7-δ, the crystal (a-b components, corrected for depinning) and powder data all reflect a nodeless gap (however, a-b symmetries remain unresolved for crystalline YBa2Cu4O8 and La1.83Sr0.17CuO4). Inconsistencies contained in multiple and noded gap interpretations of crystal data, and observed differences between bulk μ+SR and surface-sensitive measurements are discussed.
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