Perfect Absorption and Strong Coupling in Supported MoS₂ Multilayers

Abstract

Perfect absorption and strong coupling are two highly sought-after regimes of light–matter interactions. Both regimes have been studied as separate phenomena in excitonic 2D materials, particularly in MoS2. However, the structures used to reach these regimes often require intricate nanofabrication. Here, we demonstrate the occurrence of perfect absorption and strong coupling in thin MoS2 multilayers supported by a glass substrate. We measure reflection spectra of mechanically exfoliated MoS2 flakes at various angles beyond the light-line via Fourier plane imaging and spectroscopy and find that absorption in MoS2 monolayers increases up to 74% at the C-exciton by illuminating at the critical angle. Perfect absorption is achieved for ultrathin MoS2 flakes (4–8 layers) with a notable angle and frequency sensitivity to the exact number of layers. By calculating zeros and poles of the scattering matrix in the complex frequency plane, we identify perfect absorption (zeros) and strong coupling (poles) conditions for thin (<10 layers) and thick (>10 layers) limits. Our findings reveal rich physics of light–matter interactions in bare MoS2 flakes, which could be useful for nanophotonic and light harvesting applications.

Perfect Absorption at the Ultimate Thickness Limit in Planar Films

“…To confirm the PA at the t w limit, we plot the simulated reflection coefficient for the three calculated t w in three material systems, Figure 3d, where zeros are clearly obtained at or near the resonant wavelength, and there is excellent agreement between the sheet impedance 2D model and the 3D transfer matrix model. The calculated thickness t wMoSd 2 would roughly equate to four atomic layers, which aligns well with the recently reported observation of PA in MoS 2 37 (PA observed for 3 layers in the total internal reflection regime for angled TE incidence). Additionally, in Figure 3g we plot the condition eq 6 as a function of absolute wavelength and imaginary part of the permittivity and overlay the imaginary permittivities for the three materials.…”

“…For example, our bound in the Salisbury screen configuration predicts minimal PA thicknesses orders of magnitude smaller than previously derived bound for single-layer, patterned perfect absorbers, but falls within the general absorption bound derived in ref . Our predictions also align well with recent observations in TMDCs − and layered van der Waals materials, indicating that the analytical approach used here is well-suited for the ultrathin limit. Although our configuration adds significant thickness to the total structure due to the presence of a spacer, the absorption process is exclusively confined to the ultrathin layer.…”

“…Polar dielectrics such as SiC and AlN, layered van der Waals materials such as hBN and α-MoO3, and semiconductors such as GaAs and AlAs have strong TO resonances where the imaginary part of the permittivity reaches values of several hundreds, remarkably implying perfect absorption in thicknesses less than λ/1000. This result does not take into account any potential thickness dependence of the permittivity, which could play a role at such thicknesses; however optical response can remain quite strong (bulk-like), in extremely thin layers in van der Waals and/or phononic materials, down to nanoscale thicknesses. , This is especially true in monolayer and few-layer TMDCs, , indicating remarkable potential for light-matter interaction at the ultimate ultrathin limit.…”

“…This result does not take into account any potential thickness dependence of the permittivity, which could play a role at such thicknesses; however optical response can remain quite strong (bulk-like), in extremely thin layers in van der Waals and/or phononic materials, down to nanoscale thicknesses. 40,59 This is especially true in monolayer and few-layer TMDCs, 36,37 indicating remarkable potential for light-matter interaction at the ultimate ultrathin limit.…”

Probing and Control of Guided Exciton–Polaritons in a 2D Semiconductor-Integrated Slab Waveguide

“…Another approach relies on the use of high-NA oil-immersion objectives. ,, It allows imaging of the polariton dispersion in a single optical measurement but does not provide a means for controlling the parameters of the strongly coupled system and is limited to room conditions due to the use of immersion oil.…”