Weak Coupling of WSe₂ to Plasmonic Surface Lattice Resonance

Weak coupling of light emitters to optical cavities facilitates efficient photon extraction by directing their emission into cavity modes instead of random directions in free space. Monolayer transition metal dichalcogenides (TMDs) are 2D semiconductors with the direct band gap attractive for future nanoscale optoelectronics. The present experimental work investigates weak coupling of monolayer WSe₂ to a metasurface cavity, consisting of a lattice of plasmonic nanodisks and supporting surface lattice resonances (SLRs) propagating in its plane. The nanodisks were fabricated from aluminum and WSe₂ mechanically transferred on top of the cavity. Angle-resolved photoluminescence (PL) measurements show efficient light emission by WSe₂ into the SLRs. The most efficient emission appears to take place into spectrally narrow modes resulting from interference of two counter-propagating SLRs, a previously unreported behavior in metasurface cavities. The obtained results suggest the opportunity to control the interference modes via geometrical factors of the lattice and thus tune the strength of its coupling to emitters, including the possibility of strong coupling.