Presure-Induced Superconducting State of Antiferromagnetic CaFe$_2$As$_2$

TL;DR

This study investigates how pressure influences the emergence of superconductivity in CaFe$_2$As$_2$, revealing that superconductivity occurs in a narrow pressure range associated with structural coexistence and magnetic fluctuations.

Contribution

It demonstrates that superconductivity in CaFe$_2$As$_2$ is induced by quasi-hydrostatic pressure and is linked to phase coexistence and magnetic fluctuations, which was not observed under ideal hydrostatic conditions.

Findings

Superconductivity appears in a narrow pressure range with phase coexistence.

Superconductivity is associated with magnetic fluctuations in coexisting phases.

The boundary between structural phases depends on pressure history.

Abstract

The antiferromagnet CaFe$_2$As$_2$ does not become superconducting when subject to ideal hydrostatic pressure conditions, where crystallographic and magnetic states also are well defined. By measuring electrical resistivity and magnetic susceptibility under quasi-hydrostatic pressure, however, we find that a substantial volume fraction of the sample is superconducting in a narrow pressure range where collapsed tetragonal and orthorhombic structures coexist. At higher pressures, the collapsed tetragonal structure is stabilized, with the boundary between this structure and the phase of coexisting structures strongly dependent on pressure history. Fluctuations in magnetic degrees of freedom in the phase of coexisting structures appear to be important for superconductivity.