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Symmetry, distorted bandstructure, and spin-orbit coupling of (group-III) metal-monochalcogenide monolayers

The electronic structure of (group-III) metal-monochalcogenide monolayers exhibits many unusual features. Some, such as the unusually distorted upper valence band dispersion we describe as a 'caldera', are primarily the result of purely orbital interactions. Others, including spin splitting and wavefunction spin-mixing, are directly driven by spin-orbit coupling. We employ elementary group theory to explain the origins of these properties, and use a tight-binding model to calculate the phenomena enabled by them, such as band-edge carrier effective g-factors, optical absorption spectrum, conduction electron spin orientation, and a relaxation-induced upper valence band population inversion and spin polarization mechanism.