Disappearance and Survival of Superconductivity in FeSe under High Pressure

TL;DR

This study explores how superconductivity in FeSe is affected by high pressure, showing it disappears with certain media but can survive with reduced crystal thickness, highlighting the role of pressure conditions.

Contribution

It demonstrates that reducing crystal thickness preserves superconductivity under high pressure, indicating the importance of hydrostatic conditions and uniaxial stress effects.

Findings

Superconductivity disappears above ~7 GPa with glycerin or Ar as media.

Reducing crystal thickness allows superconductivity to survive above 7 GPa.

Hydrostaticity and uniaxial stress influence superconductivity in FeSe.

Abstract

Superconductivity in FeSe was investigated under high pressure through the measurements of DC magnetization by using a diamond anvil cell. We successfully observed that the disappearance of the superconductivity as a results of the appearance of the non-superconducting ortho I\hspace{-1pt}I phase above $\sim$7 GPa ($\sim$5 GPa), when Ar (glycerin) is used as the pressure transmitting media. Contrary to this, it has been found that the superconductivity even survives under pressure above 7 GPa, when the thickness ($t$) of a platelet-single crystal specimen is reduced. The survival of the superconductivity above 7 GPa is consistent with a previous observation under hydrostatic pressure by using a cubic anvil apparatus, suggesting that the hydrostaticity of the pressure is improved by reducing $t$. It is also inferred that the appearance of the ortho I\hspace{-1pt}I phase is due to uniaxial stress along the [001] direction.