Ultra-high THz-field-confinement at LaAlO3 twin walls

TL;DR

This paper demonstrates that LaAlO3 twin walls can naturally confine and guide THz and MIR light at nanoscales, enabling advanced nanophotonic applications without fabrication.

Contribution

It reveals that ferroelastic twin walls in LaAlO3 serve as natural, broadband, subwavelength light confinement structures for nanophotonics.

Findings

Electromagnetic fields at twin walls are localized to sizes 260 times smaller than wavelength.

Twin walls can concentrate or repel electromagnetic energy depending on conditions.

This provides a natural platform for broadband MIR and THz nanophotonics.

Abstract

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.