Dual-circular Raman optical activity of axial multipolar order

TL;DR

This paper introduces dual-circular Raman scattering as a novel method to detect and analyze multipolar orders, such as octupolar phases, in condensed matter physics, demonstrated through first-principles calculations on pyrite.

Contribution

It proposes and validates dual-circular Raman spectroscopy as a new experimental probe for multipolar anisotropies, linking symmetry breaking to observable optical activity.

Findings

Both $ heta$-even and $ heta$-odd axial multipolar phases show significant Raman optical activity.

First-principles calculations confirm the method's effectiveness on pyrite, an axial octupolar material.

A multipolar phonon with chiral-like displacement is key to the observed phenomena.

Abstract

Multipolar order, such as octupolar order, is a key concept in condensed matter physics, particularly in light of elusive hidden orders. However, its experimental identification remains challenging due to the absence of direct coupling to conventional external stimuli. In this study, we propose that dual-circular Raman scattering serves as a probe of multipolar anisotropies. By combining symmetry analysis with microscopic calculations, we identify that both time-reversal-even ($\theta$-even) and time-reversal-odd ($\theta$-odd) axial multipolar phases exhibit the sizable Raman optical activity as a direct consequence of multipolar symmetry breaking. The quantitative significance of the proposed response is demonstrated by the first-principles study of pyrite, a prototypical axial octupolar material. Furthermore, we reveal that a multipolar phonon, a three-dimensional and alternating displacement resembling the chiral phonon, plays a vital role in the proposed optical phenomena. Our findings open a pathway for identifying multipolar orders in various materials through dual-circular Raman spectroscopy as a sensitive and versatile probe.