Pressure-induced collapsed-tetragonal phase in SrCo2As2

TL;DR

This study investigates the pressure-induced phase transition in SrCo2As2, revealing a first-order transition to a collapsed-tetragonal phase at high pressures with no observed superconductivity up to 5.9 GPa.

Contribution

It provides detailed experimental and theoretical insights into the structural, magnetic, and electronic changes of SrCo2As2 under pressure, identifying the stable collapsed-tetragonal phase.

Findings

First-order T to cT phase transition above 6 GPa

No superconductivity observed up to 5.9 GPa

cT phase is structurally stiffer along c-axis

Abstract

We present high-energy x-ray diffraction data under applied pressures up to p = 29 GPa, neutron diffraction measurements up to p = 1.1 GPa, and electrical resistance measurements up to p = 5.9 GPa, on SrCo2As2. Our x-ray diffraction data demonstrate that there is a first-order transition between the tetragonal (T) and collapsed-tetragonal (cT) phases, with an onset above approximately 6 GPa at T = 7 K. The pressure for the onset of the cT phase and the range of coexistence between the T and cT phases appears to be nearly temperature independent. The compressibility along the a-axis is the same for the T and cT phases whereas, along the c-axis, the cT phase is significantly stiffer, which may be due to the formation of an As-As bond in the cT phase. Our resistivity measurements found no evidence of superconductivity in SrCo2As2 for p <= 5.9 GPa and T >= 1.8 K. The resistivity data also show signatures consistent with a pressure-induced phase transition for p >= 5.5 GPa. Single-crystal neutron diffraction measurements performed up to 1.1 GPa in the T phase found no evidence of stripe-type or A-type antiferromagnetic ordering down to 10 K. Spin-polarized total-energy calculations demonstrate that the cT phase is the stable phase at high pressure with a c/a ratio of 2.54. Furthermore, these calculations indicate that the cT phase of SrCo2As2 should manifest either A-type antiferromagnetic or ferromagnetic order.