Interlayer decoupling in twisted bilayers of $\beta$-phosphorus and arsenic: a computational study

We investigate magnetism and band structure engineering in Moir'e superlattice of blue phosphorus ($\beta$-P) and grey arsenene ($\beta$-As) bilayers, using $\mathit{\text{ab}}\mathit{\text{initio}}$ calculations. The electronic states near the valence and conduction band edges have significant $p_z$ character in both the bilayers. Thus, twisting the layers significantly reduce the interlayer orbital overlap, leading to a decrease in the binding energy (up to $\sim 33\mathrm{\%}$) and an increase in interlayer distance (up to $\sim 10\mathrm{\%}$), compared to the most stable AA-stacking. This interlayer decoupling also results in a notable increase (up to $\sim$25-50%) of the bandgap of twisted bilayers, with the valance band edge becoming relatively flat with van-Hove singularities in the density of states. Thus, hole doping induces a Stoner instability, leading to ferromagnetic ground state, which is more robust in Moir'e superlattices, than that of AA-stacked $\beta$-P and $\beta$-As.