Ultrastrong Coupling of Band-Nested Excitons in Few-Layer Molybdenum Disulphide

摘要

The 2D transition-metal dichalcogenides (2D TMDCs) are an intriguingplatform for studying strong light–matter interactions because they combinethe electronic properties of conventional semiconductors with the opticalresonances found in organic systems. However, the coupling strengthsdemonstrated in strong exciton–polariton coupling in the 2D TMDCs remainmuch lower than those found in organic systems. In this paper, a newapproach is taken by utilizing the large oscillator strength of the above-bandgap C exciton in few-layer molybdenum disulphide (FL-MoS_2). A k-space Rabisplitting of 293 meV is shown when coupling FL-MoS_2 C excitons to surfaceplasmon polaritons at room temperature. This value is 11 of the uncoupledexciton energy (2.67 eV or 464 nm), ≈2× what is typically seen in the TMDCs,placing the system in the ultrastrong coupling regime. The results take astep toward finally achieving the efficient quantum coherent processes ofultrastrong coupling in a CMOS-compatible system—the 2D TMDCs—in thevisible spectrum.