Transport and pinning properties of Ag-doped FeSe0.94

Abstract

We investigated the superconducting transition and the pinning properties of undoped and Ag-doped FeSe0.94 at magnetic fields up to 14 T. It was established that due to Ag addition the hexagonal phase formation in melted FeSe0.94 samples is suppressed and the grain connectivity is strongly improved. The obtained superconducting zero-field transition becomes sharp (with a transition width below 1 K), Tc and the upper critical field were found to increase, whereas the normal state resistivity significantly reduces becoming comparable with those of FeSe single crystals. In addition, a considerable magnetoresistance was observed due to Ag doping. The resistive transition of undoped and Ag-doped FeSe0.94 is dominated by thermally activated flux flow. From the activation energy U vs H dependence, a crossover from single-vortex pinning to a collective creep pinning behavior was found with increasing the magnetic field.

19 pages, 11 figures

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• Enhanced superconductivity with possible re-appearance of charge density wave states in polycrystalline Cu${}_{1-x}$Ag${}_x$Ir${}_2$Te${}_4$ alloys
• Fluctuating Cooper pairs in FeSe at temperatures exceeding double Tc