Successive spatial symmetry breaking under high pressure in the spin-orbit-coupled metal Cd2Re2O7

TL;DR

This study explores how high pressure induces multiple structural phase transitions in Cd2Re2O7, revealing successive symmetry breakings and their relation to electronic properties like superconductivity.

Contribution

It provides the first detailed high-pressure structural phase diagram of Cd2Re2O7, showing successive symmetry breakings and their connection to electronic phases.

Findings

Seven distinct structural phases identified up to 5 GPa

Inversion-symmetry breaking transition vanishes near 4 GPa

Sequential transformation into piezoelectric, ferroelectric, and centrosymmetric structures

Abstract

The 5d-transition metal pyrochlore oxide Cd2Re2O7, which was recently suggested to be a prototype of the spin-orbit-coupled metal [Phys. Rev. Lett. 115, 026401 (2015)], exhibits an inversion-symmetry breaking (ISB) transition at 200 K and a subsequent superconductivity below 1 K at ambient pressure. We study the crystal structure at high pressures up to 5 GPa by means of synchrotron X-ray powder diffraction. A rich structural phase diagram is obtained, which contains at least seven phases and is almost consistent with the electronic phase diagram determined by previous resistivity measurements. Interestingly, the ISB transition vanishes at ~4 GPa, where the enhancement of the upper critical field was observed in resistivity. Moreover, it is shown that the point groups at 8 K, probably kept in the superconducting phases, sequentially transform into piezoelectric, ferroelectric, and centrosymmetric structures on the application of pressure.