Strongly Bound Excitonic States and the Exciton Dispersion of the Layered Semiconductor BiI₃

BiI₃ is a layered semiconductor with extraordinary excitonic effects in the visible range of the optical spectra, both in the case of bulk and monolayer systems. The excitonic binding energy of bulk is to that of the paradigmatic monolayer MoS₂ and the BiI₃ monolayer has even a higher excitonic binding energy, of more than 0.5 eV. The lower dielectric screening of this trihalide material explains in part these extraordinary exciton binding energy. Therefore, this layered material has a great potential for the design of optoelectronic devices and the realization of the experiments looking for exciton physics. In addition to the interesting excitonic properties, BiI₃ is also remarkable for the strong spin-orbit interaction, which makes the material suitable to have a strong Rashba effect under electric field or to tune the spin properties using magnetic proximity effects.<br/>In this work we present a theoretical study of the electronic and optical properties of BiI₃ bulk and monolayer, within the framework of ab initio many-body perturbation theory, using the GW method and the Bethe-Salpeter Equation. We analyze the excitonic states, the influence on the spin properties of magnetic proximity effect and the possibilities to generate Rashba effect on BiI₃ monolayers. We analize also the exciton dispersion of BiI₃ bulk and monolayer, of importance to understand the exciton dynamics. Our results are very promising for experiments like time-resolved angle-resolved photoemission and other time-resolve spectroscopies.