Abstract
Non-Ising polar domain walls have recently emerged as individual two-dimensional materials exhibiting localized nonlinear optical emission. The analysis of this emitted light often requires focusing with high apertures. As a result, the vectorial properties of light come into play. This study provides an analytic treatment of the vector light fields’ effect on the polarized second-harmonic emission (SHG) arising at polar domain walls. While confined optical fields are expected to alter the SHG polarization response, we identify extrinsic and intrinsic properties capable of canceling focusing effects. We determine a precise combination of the fundamental wave polarization and orientation of the domain walls at which focusing effects are negligible. Furthermore, the perimeter defined by the domain walls intrinsic optical parameters below which focusing effects are negligible is extracted from a systematic focus-dependent analysis. Our study provides the necessary methodology and precautions to probe the internal structure of non-Ising domain walls with confined optical fields, and it can be extended to explore newly discovered ferroelectric topologic nanostructures.
Highlights
Domain walls are ultra-thin boundary regions [1] separating magnetic, ferroelectric or ferroelastic domains [2] with opposite order
We consider that there is no second-harmonic emission from the adjacent domains which is often the case in the experimental conditions chosen for polarimetry experiments on domain walls
We provide an analytic modeling of the second-harmonic generation (SHG) response of non-Ising polar domain walls taking into account the vector character of focused light as well as the local symmetry of the Néel and Blochtype walls
Summary
Domain walls are ultra-thin boundary regions [1] separating magnetic, ferroelectric or ferroelastic domains [2] with opposite order They can be polar in ferroelastic materials [3,4], show electronic conductivity [5,6,7,8,9,10,11,12,13,14] or superconductivity [15] in otherwise insulating oxides, and display enhanced local optical responses such as photovoltaic effect [16,17,18] or localized nonlinear optical emission [19,20,21,22,23,24,25] in ferroelectrics offering new perspectives for photonic applications [26]. Second-harmonic generation (SHG) microscopy has emerged as a unique method allowing the observation of the three-dimensional morphology of domain walls in technology-relevant ferroelectric photonic crystals [44,45]
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