The control and steering of light at nanometre length scales is crucial for the development of both fundamental science and nanophotonic technologies. Recent advancements have been achieved by exploiting various crystalline anisotropies, allowing for subdiffractional and diffraction-less canalisation of energy. These studies in particular benefit from stacking and twisting of 2D materials, whereas corresponding capabilities of anisotropic bulk crystals are rather unexplored. In this work, we show that ferroelastic twin walls - crystallographically perfect 2D-sheets that separate regions of differently oriented domains - in the distorted perovskite LaAlO3 provide a natural platform for broadband lateral confinement and superb canalisation of light at the nanoscale. Without fabrication processes, the electromagnetic fields localised at such walls exhibit lateral optical sizes up to 260 times smaller than the free-space wavelength. Depending on the adjacent domain orientation and frequency, the twin wall pattern preferentially concentrates or repels the electromagnetic energy, constituting a natural building block towards broadband MIR and THz nanophotonics for polaritonic circuitry.
@article{arxiv.2603.22013,
title = {Ultra-high THz-field-confinement at LaAlO3 twin walls},
author = {Jakob Wetzel and Javier Taboada-Gutiérrez and Matthias Roeper and Felix G. Kaps and Giuliano Esposito and Drini Marchese and Robin Buschbeck and Pauline Lenz and J. Michael Klopf and Hans A. Bechtel and Stephanie N. Gilbert Corder and Jeremie Teyssier and Susanne C. Kehr and Lukas M. Eng and Alexey B. Kuzmenko and Samuel D. Seddon},
journal= {arXiv preprint arXiv:2603.22013},
year = {2026}
}