Large magneto-optical effects in hole-doped blue phosphorene and gray arsenene.

Blue phosphorene (BP) and gray arsenene (GA), consisting of phosphorus and arsenic atoms in two-dimensional (2D) low-buckled honeycomb lattices, respectively, have received great interest because of their excellent electronic and optoelectronic performances. Here, using first-principles density functional theory, we investigate magneto-optical (MO) Kerr and Faraday effects in BP and GA under hole doping. Ferromagnetic ground states are found in hole-doped monolayer and bilayer BP and GA due to the Stoner electronic instability, which originates from the van Hove singularity of the density of states at the valence band edge. The Kerr and Faraday effects strongly depend on the doping concentration and therefore are electrically controllable by adjusting the number of holes via the gate voltage. The influences of the thin film thickness, spin-polarized direction, and the substrate on the MO effects are further studied. We find that the MO effects are weakened remarkably as the thin film thickness increases and can be negligible more than three single-layers; the MO effects are much more prominent when spin polarization is along the out-of-plane direction and will decrease more than one order of magnitude on turning the spin in the crystal plane; the insulating substrates with small refractive indices are favorable to generate large MO effects and appropriate compressive strains applied on BP and GA due to lattice mismatch with substrates are further beneficial. The MO effects in GA are generally larger than those in BP because the strength of spin-orbit coupling in the arsenic atom is larger than that in the phosphorus atom. Monolayer GA possesses the largest Kerr and Faraday rotation angles, which are comparable to or even larger than those of well-known MO materials such as 3d-transition-metal multilayers and compounds. Our results indicate that BP and GA are a promising material platform for MO device applications.