Odd-parity multipole order in the spin-orbit coupled metallic pyrochlore Pb$_2$Re$_2$O$_{7-\delta}$

TL;DR

This study investigates the structural phase transition in Pb2Re2O7-{ extdelta}, revealing a cubic to tetragonal transition with inversion symmetry breaking, and proposes a space group consistent with odd-parity multipole order, enhancing understanding of spin-orbit-coupled metals.

Contribution

The paper identifies the low-temperature space group of Pb2Re2O7-{ extdelta} and links it to odd-parity multipole order, providing new insights into symmetry-breaking in spin-orbit-coupled metals.

Findings

Cubic to tetragonal phase transition at 300 K

Low-temperature space group I4122 confirmed

Similarity to Cd2Re2O7 structure and order

Abstract

The pyrochlore oxide Pb2Re2O7-{\delta} (PRO) is a candidate spin-orbit-coupled metal (SOCM) that exhibits a structural phase transition with inversion symmetry breaking. In this study, we report the results of detailed X-ray diffraction (XRD) measurements on single crystals of PRO to clarify the crystal structure below the phase transition temperature at Ts = 300 K. In the XRD patterns, a clear peak splitting is observed below Ts, indicating a cubic to tetragonal transition. Based on the group-subgroup relationship and the observed reflection conditions, the space group of the low-temperature phase is proposed to be I4122, which agrees with optical second harmonic generation measurements. This space group is the same as that of the lowest temperature structure of the analogous SOCM Cd2Re2O7 (CRO), which is realized by the emergence of odd-parity multipole order. The comparison between PRO and CRO allows for advancing our understanding on the symmetry-lowering complex order exhibited by SOCMs.