The Absence of Superconductivity in Single Phase CaFe2As2 under Hydrostatic Pressure

TL;DR

This study investigates whether hydrostatic pressure induces superconductivity in CaFe2As2, finding no evidence of bulk superconductivity under truly hydrostatic conditions and suggesting non-hydrostatic effects are responsible for previous observations.

Contribution

The paper provides high-pressure susceptibility and transport data under hydrostatic conditions, clarifying the role of pressure media in inducing superconductivity in CaFe2As2.

Findings

No bulk superconductivity observed under hydrostatic pressure

Sharp phase transitions indicate hydrostatic conditions are maintained

Superconductivity likely caused by non-hydrostatic effects in prior studies

Abstract

Recent high-pressure studies found that superconductivity can be achieved under very low pressure in the parent iron arsenide compound CaFe2As2, although details of the sharpness and temperature of transitions vary between liquid medium and gas medium measurements. To better understand this issue, we performed high-pressure susceptibility and transport studies on CaFe2As2, using helium as the pressure medium. The signatures of the transitions to the low-temperature orthorhombic and collapsed tetragonal phase remained exceptionally sharp and no signature of bulk superconductivity was found under our hydrostatic conditions. Our results suggest that phase separation and superconductivity in CaFe2As2 are induced by non-hydrostatic conditions associated with the frozen liquid media.