Optical absorption enhancement in monolayer MoS₂ using Multi-order magnetic polaritons

Two-dimensional materials, unlike their bulk counterparts, exhibit many outstanding features, such as flexibility and tunability. Among them, layered molybdenum disulfide (MoS₂) can be applied as photodetectors, transistors, and solar cells. However, the light absorption is much less compared to bulk material due to the atomic thickness. In the present work, silver gratings are proposed to enhance the optical absorptance of monolayer MoS₂ with plasmonic resonances. Rigorous coupled-wave analysis shows that the maximum absorptance of the MoS₂ layer itself is increased by more than 20 times to nearly 90%. The dramatic enhancement is caused by strong coupling between the external electromagnetic waves and artificial magnetic resonance inside the structure, namely magnetic polariton (MP). Optical energy strongly confined within the grating grooves is then absorbed by the MoS₂ layer coated above. Multi-order MPs excited within grating grooves at different depths result in either broadband or narrowband absorption of monolayer MoS₂ with tunable resonance wavelengths, which can be well predicted via generalized inductor-capacitor circuit models.