Large elasto-optic effect and reversible electrochromism in multiferroic BiFeO3

TL;DR

This paper demonstrates a large, reversible electrochromic effect in BiFeO3 thin films, achieved through strain engineering, which significantly alters optical properties and offers new opportunities for photonic and acousto-optic devices.

Contribution

It introduces a novel approach to tuning optical responses in multiferroic BiFeO3 via epitaxial strain, revealing a large elasto-optic effect and reversible electrochromism without defects.

Findings

Large elasto-optic coefficient surpassing quartz

Strain-driven variation in light absorption

Reversible, electric field-controlled electrochromism

Abstract

The control of optical fields is usually achieved through the electro-optic or acousto-optic effect in single-crystal ferroelectric or polar compounds such as LiNbO3 or quartz. In recent years, tremendous progress has been made in ferroelectric oxide thin film technology - a field which is now a strong driving force in areas such as electronics, spintronics and photovoltaics. Here, we apply epitaxial strain engineering to tune the optical response of BiFeO3 thin films, and find a very large variation of the optical index with strain, corresponding to an effective elasto-optic coefficient larger than that of quartz. We observe a concomitant strain-driven variation in light absorption - reminiscent of piezochromism - which we show can be manipulated by an electric field. This constitutes an electrochromic effect that is reversible, remanent and not driven by defects. These findings broaden the potential of multiferroics towards photonics and thin film acousto-optic devices, and suggest exciting device opportunities arising from the coupling of ferroic, piezoelectric and optical responses.