Evidence for filamentary superconductivity nucleated at antiphase domain walls in antiferromagnetic CaFe2As2

Resistivity, magnetization, and microscopic As-75 nuclear magnetic resonance (NMR) measurements in the antiferromagnetically ordered state of the iron-based superconductor parent material CaFe2As2 exhibit anomalous features that are consistent with the collective freezing of domain walls. Below T* approximate to 10 K, the resistivity exhibits a peak and downturn, the bulk magnetization exhibits a sharp increase, and As-75 NMR measurements reveal the presence of slow fluctuations of the hyperfine field. These features in both the charge and spin response are strongly field dependent, are fully suppressed by H* approximate to 15 T, and suggest the presence of filamentary superconductivity nucleated at the antiphase domain walls in this material.