Anomalous Meissner effect in pnictide superconductors

Abstract

The Meissner effect has been studied in Ba(Fe0.926Co0.074)2As2 and Ba0.6K0.4Fe2As2 single crystals and compared to well known, type-II superconductors LuNi2B2C and V3Si. Whereas flux penetration is mostly determined by the bulk pinning (and, perhaps, surface barrier) resulting in a large negative magnetization, the flux expulsion upon cooling in a magnetic field is very small, which could also be due to pinning and/or surface barrier effects. However, in stark contrast with the expected behavior, the amount of the expelled flux increases almost linearly with the applied magnetic field, at least up to our maximum field of 5.5 T, which far exceeds the upper limit for the surface barrier. One interpretation of the observed behavior is that there is a field-driven suppression of magnetic pair-breaking.

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• Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• Upper critical field of high quality single crystals of KFe${}_2$As${}_2$
• Upper critical field of isoelectron substituted SrFe${}_2$(As${}_{1-x}$P${}_x$)${}_2$
• One-step method to grow Ba0.6K0.4Fe2As2 single crystals without fluxing agent
• Anisotropic magnetism, resistivity, London penetration depth and magneto-optical imaging of superconducting K0.80Fe1.76Se2 single crystals
• On the analysis of the tin-inside-H3S Mössbauer experiment
• Cluster structure of superconducting phase and the nature of peaks in the doping dependences of the London penetration depth in iron pnictides
• Anomalous local magnetic field distribution and strong pinning in CaFe1.94Co0.06As2 single crystals