Element isotopes are characterized by distinct atomic masses and nuclear spins, which can significantly influence material properties. Notably, however, isotopes in natural materials are homogenously distributed in space. Here, we propose a method to configure material properties by repositioning isotopes in engineered van der Waals (vdW) isotopic heterostructures. We showcase the properties of hexagonal boron nitride (hBN) isotopic heterostructures in engineering confined photon-lattice waves—hyperbolic phonon polaritons. By varying the composition, stacking order, and thicknesses of h10BN and h11BN building blocks, hyperbolic phonon polaritons can be engineered into a variety of energy-momentum dispersions. These confined and tailored polaritons are promising for various nanophotonic and thermal functionalities. Due to the universality and importance of isotopes, our vdW isotope heterostructuring method can be applied to engineer the properties of a broad range of materials.
Phonon polaritons provide useful opportunities, complementary to those provided by plasmon polaritons, in the study of the interaction of light with matter at small scales. The focus of this review is on phonon polaritons in low‐dimensional van der Waals (vdW) materials and heterostructures. Phonon polaritons confined in vdW materials exhibit large electromagnetic localization and are easy to hybridize with other collective modes. The extreme optical anisotropy in vdW systems produces the natural hyperbolic dispersion, enabling the access to deep subdiffractional optics and often yielding improved figures of merit over hyperbolic metamaterials. These virtues hold promises for practical nanophotonic applications, including optical sensing, super‐resolution imaging, energy and emission engineering, quantum optics, and a next generation of optical circuit elements.
more » « less- PAR ID:
- 10457661
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 8
- Issue:
- 5
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Van der Waals (vdW) materials host a variety of polaritons, which make them an emerging material platform for manipulating light at the nanoscale. Due to the layered structure of vdW materials, the polaritons can exhibit a hyperbolic dispersion and propagate as nanoscale‐confined volume modes in thin flakes. On the other hand, surface‐confined modes can be found at the flake edges. Surprisingly, the guiding of these modes in ribbons—representing typical linear waveguide structures—is widely unexplored. Here, a detailed study of hyperbolic phonon polaritons propagating in hexagonal boron nitride ribbons is reported. Employing infrared nanoimaging, a variety of modes are observed. Particularly, the fundamental volume waveguide mode that exhibits a cutoff width is identified, which, interestingly, can be lowered by reducing the waveguide thickness. Further, hybridization of the surface modes and their evolution with varying frequency and waveguide width are observed. Most importantly, it is demonstrated that the symmetrically hybridized surface mode does not exhibit a cutoff width, and thus enables linear waveguiding of the polaritons in arbitrarily narrow ribbons. The experimental data, supported by simulations, establish a solid basis for the understanding of hyperbolic polaritons in linear waveguides, which is of critical importance for their application in future photonic devices.
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