Effect of uniaxial strain on the excitonic properties of monolayer C3N: A symmetry-based analysis

In recent years, the application of mechanical stress has become a widespread experimental method to tune the electronic and optical properties of two-dimensional (2D) materials. In this work, we investigate the impact of uniaxial tensile strain along zigzag and armchair directions on the excitonic properties of graphene-like C3N, a single-layer indirect-gap material with relevant mechanical and optical properties. To do that, we develop a tight -binding Bethe-Salpeter equation framework based on a Wannier-function description of the frontier bands of the system, and use it to compute both dark and bright excitons of C3N for different applied strain configurations. Then, we use this model approach to classify excitons of pristine and strained C3N according to the crystal symmetry and to explain the appearance of bright excitons with intense optical anisotropy in strained C3N, even at small strains. Finally, the effect of strain on the exciton dispersion at small center-of-mass momenta is discussed, with special focus on the implications for 2D linear-nonanalytic dispersions.