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The interlayer exciton of van der Waals heterostructure has become a promising platform for realizing Bose-Einstein condensation and demonstrating novel excitonic devices. For increasing the critical temperature of bosonic condensation or long-range transport, the short lifetime of the interlayer excitons has to be improved by suppressing both the radiative and non-radiative recombination processes[1,2]. However, due to its out-of-plane electric dipole nature, the radiative recombination of the interlayer exciton has not yet been able to be suppressed with conventional optical approaches[3,4]. Here, we present a theoretical study on the reflective metasurface that can suppress the density of optical states for the out-of-plane dipole moment. The metasurface consists of Au nanodisks arranged in a square lattice on the Au substrate. We examined the out-of-plane dipole emitter inside the 20-nm-thick hexagonal-BN layer, which is placed on the flat surface of the 140-nm-thick SiO2 layer covering the Au disk array. We targeted the WSe2/MoSe2 interlayer exciton of which the radiation wavelength is 900 nm. Blocking the radiative decay channels of the dipole emitter to the horizontal directions as well as the vertical directions, the proposed metasurface strongly suppresses the Purcell factor down to ~0.011 at maximum (~0.018 on average), which corresponds to the enhancement of the radiative decay time as amount as ~91 times (~56 times).
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