van der Waals isotope heterostructuring showcased in engineered light-matter waves*

Element isotopes exist universally. They possess distinct atomic masses and nuclear spins and significantly influence material properties. Notably, isotopes distribute evenly in space. To explore isotope spatial heterogeneity, we propose a new materials engineering method—van der Waals (vdW) isotope heterostructuring—to configure material properties by repositioning isotopes in engineered isotopic heterostructures. We showcase vdW isotope heterostructuring in engineering confined photon-lattice waves—hyperbolic phonon polaritons—in hexagonal boron nitride (hBN) isotopic heterostructures. By varying the composition, stacking, and thicknesses of h¹⁰BN and h¹¹BN building blocks, hyperbolic phonon polaritons can be engineered into a variety of new energy-momentum dispersions. These confined and tailored polaritons are promising for various nanophotonic and thermal functionalities. Due to the universality and importance of isotopes, the method of vdW isotope heterostructuring showcased here can apply to a broad range of materials and properties.