Excitonic circular dichroism in boron–nitrogen cluster decorated graphene†

Using the first principle calculations, we propose a boron and nitrogen cluster incorporated graphene system for efficient valley polarization. The broken spatial inversion symmetry results in high Berry curvature at K and K′ valleys of the hexagonal Brillouin zone in this semiconducting system. The consideration of excitonic quasiparticles within the GW approximation along with their scattering processes using the many-body Bethe–Salpeter equation gives rise to an optical gap of 1.72 eV with an excitonic binding energy of 0.65 eV. Owing to the negligible intervalley scattering, the electrons in opposite valleys are selectively excited by left- and right-handed circularly polarized light, as evident from the oscillator strength calculations. Therefore, this system can exhibit the circular-dichroism valley Hall effect in the presence of an in-plane electric field. Moreover, such excitonic qubits can be exploited for information processing.