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Isotopic effects on in-plane hyperbolic phonon polaritons in MoO3



Jeremy Schultz, Sergiy Krylyuk, Jeffrey Schwartz, Albert Davydov, Andrea Centrone


Hyperbolic phonon polaritons (HPhPs), hybrids of light and lattice vibrations in polar dielectric crystals, empower nano-photonic applications by enabling the confinement and manipulation of light at the nanoscale. Molybdenum trioxide (α-MoO3) is a naturally hyperbolic material, meaning that its dielectric function deterministically controls the directional propagation of in-plane HPhPs within its reststrahlen bands. Strategies such as substrate engineering, nano- and hetero-structuring, and isotopic enrichment are being developed to alter the, otherwise, intrinsic dielectric functions of natural hyperbolic materials and control the confinement and propagation of HPhPs. Since isotopic disorder can limit phonon-based processes such as HPhPs , here we synthesize isotopically enriched 92MoO3 (92Mo: 99.93 %) and 100MoO3 (100Mo: 99.01 %) crystals to tune the properties and dispersion of HPhPs with respect to natural α MoO3, which is constituted by seven Mo stable isotopes. Real-space, near-field maps measured with the photothermal induced resonance (PTIR) technique enable comparisons of in plane HPhPs in α MoO3 and isotopically enriched analogues within a reststrahlen band (≈ 820 cm^-1 to ≈ 972 cm^-1). Results show that isotopic enrichment (e.g., 92MoO3 and 100MoO3) shifts the HPhP dispersion (angular wavenumber vs IR wavelength) by ≈ 12 % and ≈ +22 %, respectively, and changes the HPhP group velocities by ≈ ±20 %, while preserving their lifetimes (≈ 3.5 ps). Altogether, isotopic enrichment was found to offer fine control over the properties that determine the anisotropic in-plane propagation of HPhPs in α MoO3, which is essential to its implementation in nanophotonic applications.


2D materials, hyperbolic materials, isotopic engineering, phonon polaritons, photothermal induced resonance


Schultz, J. , Krylyuk, S. , Schwartz, J. , Davydov, A. and Centrone, A. (2024), Isotopic effects on in-plane hyperbolic phonon polaritons in MoO3, Nanophotonics, [online],, (Accessed May 26, 2024)


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Created March 4, 2024, Updated April 23, 2024