2008/07/25 by U. Welp, Ruobing Xie, R. Xie +7
Materials Science · Physics and Astronomy · #Iron-based superconductors research #Physics of Superconductivity and Magnetism #Superconductivity in MgB2 and Alloys #cond-mat.supr-con
paper · pdf · doi:10.1103/physrevb.78.140510
15 pages with 4 figures
arxiv created 2008/07/25 · openalex publication_date 2008/10/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
We present heat-capacity measurements of the upper critical fields of single-crystal NdFeAsO_1\ensuremath-xFx. In zero-magnetic field a clear step in the heat capacity is observed at Tc\ensuremath≈47 K. In fields applied perpendicular to the FeAs layers the step broadens significantly whereas for the in-plane orientation the field effects are small. This behavior is reminiscent of the CuO2-high-Tc superconductors and is a manifestation of pronounced fluctuation effects. Using an entropy conserving construction we determine the transition temperatures in applied fields and the upper critical-field slopes of \ensuremath∂Hc2c/\ensuremath∂T=\ensuremath-0.72 T/K and \ensuremath∂Hc2ab/\ensuremath∂T=\ensuremath-3.1 T/K. Zero-temperature coherence lengths of \ensuremathξab\ensuremath≈3.7 nm and \ensuremathξc\ensuremath≈0.9 nm and a modest superconducting anisotropy of \ensuremathλ\ensuremath∼4 can be deduced in a single-band model.