Disappearance And Survival Of Superconductivity In Fese Under High Pressure

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 II phase above similar to 7 GPa (similar to 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 II phase is due to uniaxial stress along the [001] direction.