Electric Field Control of Spin Orbit Coupling and Circular Photogalvanic Effect in a True Ferrielectric Crystal

TL;DR

This paper reports the discovery of true ferrielectric behavior in a hybrid crystal, demonstrating electric field control of spin-orbit coupling and circular photogalvanic effects, which advances understanding of complex dipole systems.

Contribution

It provides the first experimental evidence of true ferrielectricity in a single-phase material and shows electric field tuning of dipole states and related photogalvanic effects.

Findings

Observation of true ferrielectric behavior with asynchronous dipole switching

Electric field-induced transition from ferrielectric to ferroelectric state

Control of spin-orbit coupling and circular photogalvanic effect via electric field

Abstract

Materials possessing long range ordering of magnetic spins or electric dipoles have been the focus of condensed matter research. Among them, ferri-systems with two sublattices of unequal/noncollinear spins or electric dipoles are expected to combine the properties of ferro- and antiferro-systems, but lack experimental observations in single phase materials. This is particularly true for the ferrielectric system, since the electric dipoles usually can be redefined to incorporate the two sublattices into one, making it indistinguishable from ferroelectric. This raises doubts about whether or not ferrielectricity can be considered as an independent ferroic order. Here we report the observation of true ferrielectric behaviors in a hybrid single crystal (MV)[SbBr5] (MV2+ = N,N'-dimethyl-4,4'-bipyridinium or methylviologen), where the two electric dipole sublattices switch asynchronously, thus cannot be reduced to ferroelectric by redefining the unit cell. Furthermore, the complex dipole configuration imparts circularly polarized light sensitivity to the system. An electric field can modulate the non-collinear dipole sublattices and even induce a transition from ferrielectric to ferroelectric state, thereby tuning the helicity-dependent photocurrent. This study opens a new paradigm for the study of true irreducible ferrielectricity (a new class of polar system) and provides an effective approach to the electric field control of spin-orbit coupling and circular photogalvanic effect.