Superconductivity in CeO_1-xF_xFeAs with upper critical field of 94 T

Abstract

We have successfully synthesized Ce based oxypnictide superconductors with fluorine doping (CeO_1-xF_xFeAs) by a two step solid state reaction method. Detailed XRD and EDX confirm the crystal structure and chemical compositions. We observe that an extremely high H_c2(0) of 94 T can be achieved in the x = 0.1 composition. This increase in H_c2(0) is accompanied by a decrease in transition temperature (38.4 K in x = 0.1 composition) from 42.5 K for the x = 0.2 phase. The in-plane Ginzburg-Landau coherence length is estimated to be ~27 Å at x = 0.2 suggesting a moderate anisotropy in this class of superconductors. The Seebeck coefficient confirms the majority carrier to be electrons and strong dominance of electron-electron correlations in this multiband superconductor.