Low-Temperature Compression Unveils Unique Superconducting and Structural Behaviors in Strontium
The superconducting and structural properties of elemental strontium metal were examined under pressures up to 60 GPa at low temperatures and high pressures. Applying pressure at low temperatures reveals differences in superconducting and structural phases compared to previous reports obtained under room-temperature compression. Notably, the superconducting critical temperature exhibits a twofold increase within the pressure range of 35–42 GPa when compressed at low temperatures. This is different when compared to cooling after a room-temperature compression. Above 42 GPa, the transition width becomes significantly sharper; the low-temperature x-ray diffraction measurements under pressure indicate that this change corresponds to the Sr-III to Sr-IV transition, with the phase boundary shifting by approximately 10 GPa due to the temperature-dependent stability of the crystal structure. Furthermore, the monoclinic Sr-IV structure remains stable to much higher pressures—at least up to 60 GPa—without the emergence of the incommensurate Sr-V phase observed at room temperature. This suggests that thermal activation energy plays a critical role in overcoming the kinetic barrier to the Sr-V phase at room temperature. Based on the diffraction experiments performed at HPCAT’s 16-BM-D beamline, and the ex-situ transport measurements, we postulate the phase diagram presented in Fig.1. This work has recently been recently published in Phys. Rev B and featured as an editor’s highlight (Phys. Rev. B 110, 174519, Nov. 25, 2024. https://doi.org/10.1103/PhysRevB.110.174519)