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abstract: 'We propose the existence, via analytical derivations, novel phenomenologies, and first-principles-based simulations, of a new class of materials that are not only spontaneously optically active, but also for which the sense of rotation can be switched by an electric field applied to them– via an induced transition between the dextrorotatory and laevorotatory forms. Such systems possess electric vortices that are coupled to a spontaneous electrical polarization. Furthermore, our atomistic simulations provide a deep microscopic insight into, and understanding of, this class of naturally optically active materials.'
author:
- 'Sergey Prosandeev$^{1,2}$, Andrei Malashevich$^{3}$, Zhigang Gui$^{1}$, Lydie Louis$^{1}$, Raymond Walter$^{1}$, Ivo Souza$^{4}$ and L. Bellaiche$^{1}$'
title: Natural optical activity and its control by electric field in electrotoroidic systems
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Introduction
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The speed of propagation of circularly-polarized light traveling inside an [*optically active*]{} material depends on its helicity [@Melrose; @Barron]. Accordingly, the plane of polarization of linearly polarized light rotates by a fixed amount per unit length, a phenomenon known as [*optical rotation*]{}. One traditional way to make materials optically active is to take advantage of the Faraday effect, by applying a magnetic field. However, there are some specific systems that are [*naturally gyrotropic*]{}, that is they spontaneously possess optical 