{"id":1874,"date":"2015-07-05T18:32:02","date_gmt":"2015-07-06T01:32:02","guid":{"rendered":"http:\/\/physikon.net\/?p=1874"},"modified":"2024-08-24T19:14:11","modified_gmt":"2024-08-25T02:14:11","slug":"1874","status":"publish","type":"post","link":"http:\/\/physikon.net\/?p=1874","title":{"rendered":"Concerning the Superconducting Gap Symmetry in YBa2<\/sub>Cu3<\/sub>O7\u2013\u03b4<\/sub>, YBa2<\/sub>Cu4<\/sub>O8<\/sub>, and La2\u2013x<\/sub>Srx<\/sub>CuO4<\/sub> Determined from Muon Spin Rotation in Mixed States of Crystals and Powders"},"content":{"rendered":"

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Concerning the Superconducting Gap Symmetry in YBa2<\/sub>Cu3<\/sub>O7\u2013\u03b4<\/sub>, YBa2<\/sub>Cu4<\/sub>O8<\/sub>, and La2\u2013x<\/sub>Srx<\/sub>CuO4<\/sub>\u00a0Determined from Muon Spin Rotation in Mixed States of Crystals and Powders<\/strong>, D. R. Harshman and A. T. Fiory\u00a0[arXiv<\/a>]\n

Muon spin rotation (\u03bc+<\/sup>SR) measurements of square root second moments of local magnetic fields \u03c3 in superconducting mixed states, as published for oriented crystals and powder samples of YBa2<\/sub>Cu3<\/sub>O7\u2013\u03b4<\/sub> (\u03b4 \u2248 0.05), YBa2<\/sub>Cu4<\/sub>O8<\/sub> and La2-x<\/sub>Srx<\/sub>CuO4<\/sub> (x ~ 0.15\u20130.17), are subjected to comparative analysis for superconducting gap symmetry. \u00a0For oriented crystals it is shown that anomalous dependences of \u03c3 on temperature and applied field H, as-measured and extracted a<\/em>– and b<\/em>-axial components, are attributable to fluxon depinning and disorder that obscure the intrinsic character of the underlying superconducting penetration depth. \u00a0Random averages derived from oriented crystal data differ markedly from corresponding non-oriented powders, owing to the weaker influence of pinning in high-quality crystals. \u00a0Related indicators for pinning perturbations such as non-monotonic H dependence of \u03c3, irreproducible data and strong H dependence of apparent transition temperatures, are also evident. \u00a0Strong intrinsic pinning suppresses thermal anomalies in c<\/em>-axis components of \u03c3, which reflect nodeless gap symmetries in YBa2<\/sub>Cu3<\/sub>O7\u2013\u03b4<\/sub> and YBa2<\/sub>Cu4<\/sub>O8<\/sub>. For YBa2<\/sub>Cu3<\/sub>O7\u2013\u03b4<\/sub>, the crystal (a<\/em>–b<\/em> components, corrected for depinning) and powder data all reflect a nodeless gap (however, a<\/em>–b<\/em> symmetries remain unresolved for crystalline YBa2<\/sub>Cu4<\/sub>O8<\/sub> and La1.83<\/sub>Sr0.17<\/sub>CuO4<\/sub>. \u00a0Inconsistencies contained in multiple and noded gap interpretations of crystal data, and observed differences between bulk\u00a0\u03bc+<\/sup> and surface-sensitive measurements are discussed.<\/p>\n

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Root second moment data for YBa2<\/sub>Cu3<\/sub>O7\u2013δ<\/sub> specimens. The triangles represent the average of the single crystal field-oriented data. The diamonds and circles correspond to the non-oriented powder data sets \"A\u201d (H = 0.35 T) and \u201cB\u201d (H = 0.2 T), respectively. The solid and dashed curves through the data represent fits of our pinning model assuming a two-fluid form for the gap function. Inset: Plot of fitted \"two-fluid\" exponent \u03b1 versus Tc for oxygen-deficient YBa2<\/sub>Cu3<\/sub>O7\u2013\u03b4<\/sub>. The dashed line denotes the trend.<\/p><\/td>

\"Figure-2\"<\/a>
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D. R. Harshman and A. T. Fiory, J. Phys.: Condens. Matter 23<\/strong>, 315702 (2011)<\/a>.<\/p>\n

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