A parity-breaking electronic nematic phase transition in the spin-orbit coupled metal Cd$_2$Re$_2$O$_7$

TL;DR

This paper reports the discovery of a novel parity-breaking multipolar nematic phase in the spin-orbit coupled metal Cd$_2$Re$_2$O$_7$, revealing new symmetry-breaking phenomena driven by electron interactions.

Contribution

It identifies a unique multipolar nematic phase with parity-breaking properties in a strongly spin-orbit coupled metal, expanding understanding of correlated electron phases.

Findings

Discovery of a multipolar nematic phase in Cd$_2$Re$_2$O$_7$

The phase breaks rotational symmetry and is odd under inversion

The phase transition occurs near 200 K and induces lattice distortion

Abstract

Strong electron interactions can drive metallic systems toward a variety of well-known symmetry-broken phases, but the instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncovered a multipolar nematic phase of matter in the metallic pyrochlore Cd$_2$Re$_2$O$_7$ using spatially resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic nematic phases, this multipolar phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of the multipolar nematic order parameter, we show that it drives the thermal phase transition near 200 kelvin in Cd$_2$Re$_2$O$_7$ and induces a parity-breaking lattice distortion as a secondary order.