Excitons and trions in monolayer semiconductors with correlated electrons

Abstract: We revisit low-temperature optical spectra of transition-metal dichalcogenide monolayers and point to a possible crystallization of electrons (or holes) at low to moderate charge densities. To calculate the excitonic spectra under such conditions, we introduce the recursion method and compute how the charge density affects the energies, linewidths, and oscillator strengths of exciton and trion complexes. Equally important, we study how excitons and trions in the monolayer evolve when the charge particles gradually transition to a periodic Wigner lattice. The results provide valuable information on the ability to detect whether the particles are ordered through the exciton spectrum. Finally, we calculate the change in exciton energy in cases that the added charge particles have similar and dissimilar quantum numbers (spin and valley) to those of the electron or hole in the exciton. The results of this work shed new light on important optical properties of monolayer semiconductors.