Stacking-dependent electronic properties of few-layer and bulk γ-GeSe from GW approximation*

The group-IV monochalcogenide has attracted interest due to its potentials of ferroelectric and multiferroic properties. Recently, centrosymmetric γ-phase GeSe in the double-layer honeycomb lattice was theoretically predicted, but synthesized γ-phase GeSe showed noncentrosymmetric atomic structure, opening a chance for ferroelectricity and spin-splitting. In our present work, we study electronic band structures of the centrosymmetric and noncentrosymmetric few-layer and bulk γ-GeSe using density functional theory and GW calculations [1]. We discuss stacking-dependent band gaps, spontaneous polarizations, and spin-splitting in centrosymmetric and noncentrosymmetric γ-GeSe which show different stacking sequences of atomic layers. We also investigate ferroelectric switching pathways, ferroelectric energy barriers, and origin of spontaneous polarizations in γ-GeSe from its unique stacking geometries.