Based on extensive first principle calculations, we explore the thickness dependent effective dielectric constant and slab polarizability of few layer black phosphorene. We find that the dielectric constant in ultra-thin phosphorene is thickness dependent and it can be further tuned by applying an out of plane electric field. The decreasing dielectric constant with reducing number of layers of phosphorene, is a direct consequence of the lower permittivity of the surface layers and the increasing surface to volume ratio. We also show that the slab polarizability depends linearly on the number of layers, implying a nearly constant polarizability per phosphorus atom. Our calculation of the thickness and electric field dependent dielectric properties will be useful for designing and interpreting transport experiments in gated phosphorene devices, wherever electrostatic effects such as capacitance, charge screening etc. are important.
Two dimensional magnetic materials, with tunable electronic properties could lead to new spintronic, magnetic and magneto-optic applications. Here, we explore intrinsic magnetic ordering in two dimensional monolayers of transition metal tri-halides (MX 3 , M = V, Cr, Mn, Fe and Ni, and X = F, Cl, Br and I), using density functional theory. We find that other than FeX 3 family which has an anti-ferromagnetic ground state, rest of the trihalides are ferromagnetic. Amongst these the VX 3 and NiX 3 family are found to have the highest magnetic transition temperature, beyond the room temperature. In terms of electronic properties, the tri-halides of Mn and Ni are either half metals or Dirac half metals, while the tri-halides of V, Fe and Cr are insulators. Among all the trihalides studied in this paper, we find the existence of very clean spin polarized Dirac half metallic state in MnF 3 , MnCl 3 , MnBr 3 , NiF 3 and NiCl 3 . These spin polarized Dirac half metals will be immensely useful for spin-current generation and other spintronic applications. arXiv:1905.13677v1 [cond-mat.mtrl-sci]
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