Magnetic field effects and excitonic selection rules in monolayer palladium diselenide as a large-gap quantum spin Hall insulator

Quantum spin hall (QSH) effect, a class of quantum state, is promising for dissipationless transport with topologically protected helical edge state. Based on first-principles calculations, we theoretically demonstrate the topological physics of 1H-PdSe2 with a large gap up to 0.24 eV. The band inversion takes place either among the pz and px,y orbitals of Se atom or due to spin-orbital coupling under compressive strains. The edge modes exist in the energy gap and can be characterized by an effective edge state Hamiltonian. Based on the derived two-band k center dot p model, we demonstrate the profound phenomena induced by the applied magnetic field effects and optical transitions for chiral fermions, which lead to complicated excitonic selection rules in this topologically nontrivial two-dimensional material. Our results will pave the way for future theoretical and experimental studies on PdX2 (X = S,Se,Te) monolayers.