Fig. 1: Schematic illustration of the considered system and the band structure of atomic monolayer.

a Sketch of the structure. A hBN-encapsulated TMD monolayer hosting excess electrons is embedded in an optical microcavity in the presence of a normal-to-plane uniform magnetic field. The microcavity is filled with dielectric media represented by PMMA. A pair of electrodes consisting of a metallic gate and graphene layer is used to control the density of excess electrons. A cavity photon creates an electron-hole pair, which is associated with a free electron forming a three-particle bound state (a trion). The radiative recombination of a trion generates a cavity photon and a free electron. In high-Q optical cavity, a successive repetition of these processes leads to the onset of strong light-matter coupling regime and formation of hybrid states, trion-polaritons. b Band structure in the vicinity of ±K points of Brillouin zone and optical excitonic transition (thick arrow) in WSe₂ monolayer in the presence of free electron gas. The arrows indicate the subband’s spin projection. The lowest-energy trion state in the -K valley is formed by an electron from the upper conduction subband and a hole from the upper valence subband, coupled with an excess electron, located in the +K valley of the lower conduction subband.