Electric Field-Manipulated Optical Chirality in Ferroelectric Vortex Domains

Manipulating optical chirality via electric fields has garnered significant attention in both fundamental physics and practical applications. Chiral ferroelectrics, characterized by their inherent optical chirality and switchable spontaneous polarization, have emerged as a promising platform for electronic-photonic integrated circuits. Despite notable advancements in the realm of chirality within organics, the progress in inorganic ferroelectrics has been comparatively sluggish, primarily attributed to the scarcity of chiral centers in these materials. Recently, by introducing polar topological textures through discontinuous interface in heterostructures [Nature 2019, 568, 368-372.], chirality has been successfully achieved in inorganics. However, the generalizability of this approach, which is contingent on the discontinuity of the interface, has yet to be explored across different material systems, and detecting chirality stemming from polar topological textures is challenging, highlighting the necessity for further investigation in this area.
Ferroelectrics nanoislands have long been recognized for their unique size-confined mechanical, electrical and geometric boundary conditions, making them attractive for exploring novel polar topological structures, as well as optical chirality. By utilizing the self-assembly growth strategy, we have successfully stabilized polar Solomon domains [Nat. Commun. 2023, 14, 3941.] and center-type quad-domains [Nat. Nanotechnol. 2018, 13, 947-952.] in BiFeO₃ (BFO) nanoislands with the lateral size of 200-600 nm. Additionally, the domains and domain walls can be deterministically manipulated by external electric fields [Nat. Commun. 2023, 13, 3255; Acta Mater. 2019, 175, 324-330.]. Expanding upon our previous research, we recently proposed an innovative protocol for stabilizing ferroelectric vortex domains in BFO-based nanoislands, and reported the first observation of optical chirality in spontaneously stabilized vortex domains within a single-phase ferroelectric material [Adv. Mater. 2024, 2408400.], rather than a heterostructure. By integrating the piezoresponse force microscopy and nonlinear optical second-harmonic generation probes, the correlation between chirality and ferroelectric vortex domains in these BFO nanoislands is explicitly established. Capitalizing on the synergistic coupling between ferroelectricity and chirality, we achieved a reversible and nonvolatile electric field-controllable chiral transformation. The self-assembly BFO nanoislands, serving as discrete chiral units, are integrated into ordered arrays and exhibit capabilities in chiral optical display functionalities. This achievement represents a significant step forward in chirality manipulation within simple inorganic material systems through electrical means, which could have potential implications for the development of advanced optoelectronic devices.