Novel two-dimensional van der Waals materials: layered IV-V compounds

Since the successful exfoliation of graphene from graphite, a variety of two-dimensional (2D) van der Waals (vdW) materials have also been emerged and extensively studied over the last decade. Nevertheless there have been continuing demand for new 2D vdW materials that can exhibit unusual physical properties. Here, we propose layered IV-V compounds as novel 2D vdW materials based on our first-principles calculations. Our predicted IV-V compounds are in the form of A₂B₂, where A and B are elements in group IV or 14 (C, Si, Ge, Sn) and group V or 15 (N, P, As, Sb), respectively. These structures are similar to those of layered III-VI compounds, such as GaSe or InSe. Our investigation reveals that newly-discovered compounds have two distinguishable phases, α and β, which have a mirror and an inversion symmetry. To explore their structural stabilities and their phase transitions from one phase to the other, we perform geometrical optimization; evaluate their phonon dispersion relations; and estimate activation barrier of the phase transitions. We further investigate their electronic properties by calculating not only their electronic band structures, but also carrier transport properties including electron-phonon interaction.