Analytical approach to excitonic properties of MoS2

We present an analytical investigation of the optical absorption spectrum of monolayer molybdenumdisulfide. Based on the density matrix formalism, our approach gives insights into the microscopic origin of excitonic transitions, their relative oscillator strength, and binding energy. We show analytical expressions for the carrier-light coupling element, which contains the optical selection rules and well describes the valleyselective polarization in MoS2. In agreement with experimental results, we find the formation of strongly bound electron-hole pairs due to the efficient Coulomb interaction. The absorption spectrum of MoS2 on a silicon substrate features two pronounced peaks at 1.91 eV and 2.05 eV corresponding to the A and B exciton, which are characterized by binding energies of 420 meV and 440 meV, respectively. Our calculations reveal their relative oscillator strength and predict the appearance of further low-intensity excitonic transitions at higher energies. The presented approach is applicable to other transition metal dichalcogenides and can be extended to investigations of trion and biexcitonic effects.