Evidence for filamentary superconductivity nucleated at antiphase domain walls in antiferromagnetic CaFe$_2$As$_2$

TL;DR

This study presents evidence that filamentary superconductivity occurs at antiphase domain walls in CaFe$_2$As$_2$, revealed through resistivity, magnetization, and NMR measurements showing anomalous low-temperature features.

Contribution

It provides experimental evidence for filamentary superconductivity nucleated specifically at antiphase domain walls in CaFe$_2$As$_2$, a parent iron-based superconductor.

Findings

Resistivity shows a peak and downturn below 10 K.

Magnetization sharply increases below 10 K.

NMR detects slow hyperfine field fluctuations.

Abstract

Resistivity, magnetization and microscopic $^{75}$As nuclear magnetic resonance (NMR) measurements in the antiferromagnetically ordered state of the iron-based superconductor parent material CaFe$_2$As$_2$ exhibit anomalous features that are consistent with the collective freezing of domain walls. Below $T^*\approx 10$ K, the resistivity exhibits a peak and downturn, the bulk magnetization exhibits a sharp increase, and $^{75}$As 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 $H^*\approx 15$ T, and suggest the presence of filamentary superconductivity nucleated at the antiphase domain walls in this material.