Ferroelectric solitons crafted in epitaxial bismuth ferrite superlattices

Abstract

In ferroelectrics, complex interactions among various degrees of freedom enable the condensation of topologically protected polarization textures. Known as ferroelectric solitons, these particle-like structures represent a new class of materials with promise for beyond-CMOS technologies due to their ultrafine size and sensitivity to external stimuli. Such polarization textures have scarcely been demonstrated in multiferroics. Here, we present evidence for ferroelectric solitons in (BiFeO3)/(SrTiO3) superlattices. High-resolution piezoresponse force microscopy and Cs-corrected high-angle annular dark-field scanning transmission electron microscopy reveal a zoo of topologies, and polarization displacement mapping of planar specimens reveals center-convergent/divergent topological defects as small as 3 nm. Phase-field simulations verify that some of these structures can be classed as bimerons with a topological charge of ±1, and first-principles-based effective Hamiltonian computations show that the coexistence of such structures can lead to non-integer topological charges, a first observation in a BiFeO3-based system. Our results open new opportunities in multiferroic topotronics.

Structural and Chemical Insights into Designer Defects in Tetragonal-like Epitaxial BiFeO3 Thin Films

“…These inclusions, which are coherent with the matrix, were intentionally randomly dispersed throughout the BFO phase by careful control of the thin film deposition conditions. Such designer defect inclusions not only help to maintain the high crystalline quality of the T’ BFO phase but also enable an almost perfectly reversible phase transformation between T’ and R’ BFO using a local applied electric field as well as the longest reported nanoscale domain stability in a thin film ferroelectric system. , More recently, we have shown that they can assist in the formation of ferroelectric solitons in superlattices of BFO-SrTiO 3 (STO) and influence the temperature-dependent spin Hall magnetoresistance of epitaxial BFO . Note that the stabilization of T’ BFO by BO phases is not restricted to growth on LAO substrates alone.…”

Tuning the Photonic Spectrum of Superlattice Structures with Magnetic Fields: An Anisotropic Perspective

“…Thus, the study of using magnetic fields in superlattices can be seen as a possible way to design and generate new optical devices for future all-optical technologies. Recently, even the influence of randomness has been studied in similar optical devices [12], and nonlinear modes such as ferroelectric solitons in epitaxial bismuth ferrite superlattices have been successfully observed in experimental setups [13]. In a standard approach, it is assumed that such an external magnetic field points in one constant direction, and then one studies how the strength of this field affects the way that light behaves in the superlattice system.…”