Ultralow-loss polaritons in isotopically pure boron nitride

Abstract

Conventional optical components are limited to size scales much larger than the wavelength of light, as changes to the amplitude, phase and polarization of the electromagnetic fields are accrued gradually along an optical path. However, advances in nanophotonics have produced ultrathin, so-called 'flat' optical components that beget abrupt changes in these properties over distances significantly shorter than the free-space wavelength. Although high optical losses still plague many approaches, phonon polariton (PhP) materials have demonstrated long lifetimes for sub-diffractional modes in comparison to plasmon-polariton-based nanophotonics. We experimentally observe a threefold improvement in polariton lifetime through isotopic enrichment of hexagonal boron nitride (hBN). Commensurate increases in the polariton propagation length are demonstrated via direct imaging of polaritonic standing waves by means of infrared nano-optics. Our results provide the foundation for a materials-growth-directed approach aimed at realizing the loss control necessary for the development of PhP-based nanophotonic devices.

Isotopic effects on phonon anharmonicity in layered van der Waals crystals: Isotopically pure hexagonal boron nitride

“…This provides opportunities for reducing the optical losses in hyperbolic phonon-polariton devices, where the phononpolariton modal lifetimes are on the order of the lifetimes of the optical phonons themselves [2]. Indeed, ultralow-loss polaritons have been recently reported in isotopically pure boron nitride [10]. Another area in which isotopic enrichment plays a crucial role is the development of high-efficiency solid-state neutron detectors.…”

“…Another area in which isotopic enrichment plays a crucial role is the development of high-efficiency solid-state neutron detectors. The 10 B isotope has a very large capture cross-section for thermal neutrons, and detectors based on 10 B enriched (99.9%) h-BN have demonstrated the highest detection efficiency (51.4%) for solid-state detectors to date [11].…”

“…h-BN has also great potential for solid-state neutron detection and neutron imaging devices, given the exceptionally high thermal neutron capture cross section of the boron-10 isotope. A good knowledge of phonons in layered crystals is essential for harnessing long-lived phonon-polariton modes for nanophotonic applications and may prove valuable for developing solidstate 10 BN neutron detectors with improved device architectures and higher detection efficiencies. Although phonons in graphene and isoelectronic materials with a similar hexagonal layer structure have been studied, the effect of isotopic substitution on the phonons of such lamellar compounds has not been addressed yet.…”

“…Here we present a Raman scattering study of the in-plane high-energy Raman active mode on isotopically enriched singlecrystal h-BN. Phonon frequency and lifetime are measured in the 80-600-K temperature range for 10 B-enriched, 11 B-enriched, and natural composition high quality crystals. Their temperature dependence is explained in the light of perturbation theory calculations of the phonon self-energy.…”

“…The effects of crystal anisotropy, isotopic disorder, and anharmonic phonon-decay channels are investigated in detail. The isotopic-induced changes in the phonon density of states are shown to enhance three-phonon anharmonic decay channels in 10 B-enriched crystals, opening the possibility of isotope tuning of the anharmonic phonon decay processes. DOI: 10.1103/PhysRevB.97.155435…”