High-pressure Raman study on the superconducting pyrochlore oxide Cd2Re2O7

The superconducting pyrochlore oxide Cd₂Re₂O₇ ($T_c=1K$), which is now considered as a candidate of the spin-orbit-coupled metal, shows an inversion-symmetry-breaking structural transition at $T_{s1}=200K$. $T_{s1}$ decreases with increasing pressure and disappears at around $P_c=4.2\mathrm{GPa}$, where at least four high-pressure phases with tiny structural distortions are suggested by means of powder X-ray diffraction [Yamaura PRB 2017]. We have carried out Raman scattering experiments to investigate changes in the crystal symmetry under high pressures up to 4.8 GPa. A structural transition at 1.9–3.0 GPa and the recovery of inversion symmetry above $P_c$ are observed at 12 K.