Effect of low-temperature compression on superconductivity and crystal structure in strontium metal

TL;DR

This study explores how applying pressure to strontium metal at cryogenic temperatures affects its superconducting properties and crystal structure, revealing enhanced superconductivity and phase stability compared to room temperature conditions.

Contribution

It demonstrates that low-temperature compression alters phase transitions and superconducting behavior, notably increasing Tc and stabilizing the Sr-IV phase up to higher pressures.

Findings

Superconducting Tc doubles under cryogenic compression in 35-42 GPa range.

Transition sharpness increases above 42 GPa, indicating phase change.

Sr-IV structure remains stable up to 60 GPa without forming Sr-V phase.

Abstract

The superconducting and structural properties of elemental strontium metal were investigated under pressures up to 60 GPa while maintaining cryogenic conditions during pressure application. Applying pressure at low temperatures reveals differences in superconducting and structural phases compared to previous reports obtained at room temperatures. Notably, the superconducting critical temperature exhibits a twofold increase under compression after cryogenic cooling within the pressure range of 35-42 GPa, compared to cryogenic cooling after room-temperature compression. Subsequently, the transition width becomes significantly sharper above 42 GPa. Low-temperature X-ray diffraction measurements under pressure reveal that this change corresponds to the Sr-III to Sr-IV transition, with no evidence of any metastable structure. Furthermore, the monoclinic Sr-IV structure was observed to remain stable to much higher pressures - at least up to 60 GPa, without the appearance of the incommensurate Sr-V phase present at room temperature. This implies that thermal activation energy plays an important role in overcoming the presence of a kinetic barrier to the Sr-V phase at room temperature.