Concerning the superconducting gap symmetry in YBa2Cu3O7-{\delta},   YBa2Cu4O8, and La2-xSrxCuO4 determined from muon spin rotation in mixed   states of crystals and powders
  Muon spin rotation ({\mu}+SR) measurements of square-root second moments of local magnetic fields {\sigma} in superconducting mixed states, as published for oriented crystals and powder samples of YBa2Cu3O7-{\delta} ({\delta} {\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 {\sigma} 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 {\sigma}, irreproducible data and strong H dependence of apparent transition temperatures are also evident. Strong intrinsic pinning suppresses thermal anomalies in c-axis components of {\sigma}, which reflect nodeless gap symmetries in YBa2Cu3O7-{\delta} and YBa2Cu4O8. For YBa2Cu3O7-{\delta}, 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 {\mu}+SR and surface-sensitive measurements are discussed. 
Dale R. Harshman (1 and 2) and Anthony T. Fiory (3) ((1) Physikon   Research Corporation, (2) Dept. of Physics, University o...
cond-mat.supr-con