Vacancy-Engineered Phonon Polaritons in \(\alpha\)-MoO\(_3\)

Low-symmetry van der Waals materials have enabled strong confinement of mid-infrared light through hyperbolic phonon polaritons (HPhPs) at the nanoscale. Yet, the bottleneck persists in manipulating the intrinsic polaritonic dispersion to drive further progress in phonon-polaritonics. Here, we prese...

Full description

Saved in:
Bibliographic Details
Published in:arXiv.org 2023-09
Main Authors: Hussain, Naveed, Mashnoon Alam Sakib, Li, Zhaoxu, Harris, William, Ahmed, Shehzad, Wu, Ruqian, Wickramasinghe, H Kumar, Shcherbakov, Maxim R
Format: Article
Language:English
Subjects:
Density functional theory
Dispersion
Flakes (defects)
Group velocity
Hot pressing
Image resolution
Infrared radiation
Permittivity
Phonons
Polaritons
Stoichiometry
Thermal imaging
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Low-symmetry van der Waals materials have enabled strong confinement of mid-infrared light through hyperbolic phonon polaritons (HPhPs) at the nanoscale. Yet, the bottleneck persists in manipulating the intrinsic polaritonic dispersion to drive further progress in phonon-polaritonics. Here, we present a thermomechanical strategy to manipulate the HPhPs in \(\alpha\)-MoO\(_3\) using high pressure and temperature treatment. The hot pressing engineers the stoichiometry of \(\alpha\)-MoO\(_3\) by controllably introducing oxygen vacancy defects (OVDs), which cause a semiconductor-to-semimetal transition. Our density functional theory and finite-difference time-domain results, combined with experimental studies show that the OVDs induce a metastable metallic state by reducing the bandgap while modifying the intrinsic dielectric permittivity of \(\alpha\)-MoO\(_3\). Photo-induced force microscopy confirms an average dielectric permittivity tunability of \(|\Delta\varepsilon/\varepsilon|\approx0.35\) within a Reststrahlen band of \(\alpha\)-MoO\(_3\), resulting in drastic shifts in the HPhP dispersion. The polariton lifetimes for pristine and hot-pressed flakes were measured as \(0.92 \pm 0.06\) and \(0.86 \pm 0.11\) ps, respectively, exhibiting a loss of only 7%, while the group velocity exhibited an increase of \(38.8 \pm 0.2\)%. The OVDs in \(\alpha\)-MoO\(_3\) provide a low-loss platform that enables active tuning of mid-infrared HPhPs and have a profound impact on applications in super-resolution imaging, nanoscale thermal manipulation, boosted molecular sensing, and on-chip photonic circuits.
ISSN:2331-8422