Crystal structure of the inversion-breaking metal Cd2Re2O7

TL;DR

This paper investigates the crystal structure of Cd2Re2O7, linking inversion-breaking transition phenomena observed in SHG, neutron, and x-ray diffraction data, and discusses implications for improper ferroelectricity.

Contribution

It provides a structural explanation for inversion-breaking transition in Cd2Re2O7, integrating multiple experimental data types and proposing future experiments.

Findings

Structural scenario explains reflection extinctions in x-ray data

Inversion-breaking transition involves three order parameters

Relation to Landau theory and improper ferroelectrics

Abstract

Second harmonic generation (SHG) on the pyrochlore metal Cd2Re2O7 indicates the presence of three order parameters setting in below an inversion breaking transition. Here, we explore a possible structural explanation and relate it not only to the SHG data, but also to neutron and x-ray diffraction, where we find that such a structural scenario can explain certain reflection extinctions observed in single crystal x-ray data. From this analysis, we suggest future experiments that could be done to resolve this matter. Finally, we comment on the Landau-violating nature of the inversion breaking transition and its relation to similar phenomena observed in improper ferroelectrics.