Excitons and trions in two-dimensional semiconductors based on transition metal dichalcogenides
Ioffe Institute, Russian Academy of Sciences, ul. Polytekhnicheskaya 26, St. Petersburg, 194021, Russian Federation
Theoretical and experimental results on excitonic effects in monomolecular layers of transition metal dichalcogenides are reviewed. These two-dimensional semiconductors exhibit a direct band gap of about 2 eV at the Brillouin zone edges, and the binding energies of their neutral and charged excitons are in the range of hundreds and tens of millielectronvolts, respectively. This implies that the electron-hole complexes determine the optical properties of transition metal dichalcogenide monolayers. Topics discussed in this review include the band structure details needed to understand the excitonic effects in these materials, the structure and fine structure of excitons and trions, the features of the spin and valley dynamics of Coulomb complexes, and the ways how neutral and charged excitons manifest themselves in linear and nonlinear optical effects.