Evidence for distortion-induced local electric polarization in $\alpha$-RuCl$_3$

TL;DR

This study reveals that distortions in $ ext{α}$-RuCl$_3$ induce local electric polarization linked to charge redistribution and spin correlations, highlighting charge effects in Kitaev materials.

Contribution

It demonstrates the presence of distortion-induced local electric polarization in $ ext{α}$-RuCl$_3$, a novel finding connecting charge effects with spin correlations in this Kitaev candidate.

Findings

Electric polarization appears at room temperature in $ ext{α}$-RuCl$_3$.

Short-range spin correlations enhance electric polarization.

Charge redistribution occurs via virtual hopping and charge dimerization.

Abstract

The spin-orbit assisted Mott insulator $\alpha$-RuCl$_3$ is a prime candidate for material realization of the Kitaev quantum spin liquid. While little attention has been paid to charge degrees of freedom, charge effects, such as electric polarization, may arise in this system. Here, we report distortion-induced local electric polarization in $\alpha$-RuCl$_3$ as evidenced by single-crystal X-ray diffraction, second harmonic generation (SHG) and dielectric measurements. The SHG signal appears at room temperature and develops substantially in the Kitaev paramagnetic state when short-range spin correlations come into play. Despite sizable pyroelectric currents in the Kitaev paramagnetic state, the absence of hysteresis in electric field-dependent polariza-tion (P-E) points to the short-range nature of electric polarization. This localized electric polarization is likely the result of distortion-induced charge dimerization, achieved through virtual hopping-induced charge redistribution. In addition, the electric polarization is boosted by short-range spin correlations via spin-phonon coupling in the Kitaev paramagnetic state. Our results emphasize the importance of charge degrees of freedom in $\alpha$-RuCl$_3$, which establish a novel platform to investi-gate charge effects in Kitaev materials.