Contrary to empirical observations, lowest-order k⋅p^ theory predicts that monolayer black phosphorus ("phosphorene") is completely immune to zigzag-polarized optical excitation at the bandgap energy. Using symmetry arguments, we derive a 2×2 Hamiltonian under the k⋅p^ formalism including higher-order corrections, which is used to show that the experimentally-measured band-gap transition with zigzag polarization is dominated by the third order k⋅p^ perturbation in the interband optical matrix element, whereas the effects of spin-orbit interaction are negligible in this material, consistent with a trivial orbital diamagnetic contribution to the g-factor.
@article{arxiv.1908.10837,
title = {Origins of electromagnetic anisotropy in monolayer black phosphorus},
author = {Pengke Li},
journal= {arXiv preprint arXiv:1908.10837},
year = {2019}
}