Excitonic and magneto-optical effects in Kagome monolayer Nb3X8 (X= Cl, Br, and I)

Kagome monolayers, prized for their unique physical properties, have emerged as promising candidates for the fabrication of advanced functional devices. Here, we investigate excitonic effects and the magneto-optical Kerr effect in monolayer Nb₃X₈ (X = Cl, Br, I) by solving the Bethe-Salpeter equation on top of GW-corrected electronic structures. Our results reveal exceptionally high exciton binding energies in Nb₃X₈, exceeding those of transition metal dichalcogenides. Notably, Nb₃Cl₈ exhibits a binding energy of up to 1.137 eV, with its exciton wavefunction highly localized within a unit cell. Additionally, the halogen atom significantly influences the amplitude of the Kerr spectrum, and excitonic effects shift its energy threshold. These findings provide valuable insights into potential applications in optical and magneto-optical devices.