SnP₃: A Previously Unexplored Two-Dimensional Material

We predict SnP₃ to be an easily exfoliable and dynamically stable two-dimensional (2D) material with thickness-dependent electronic properties. On the basis of density functional theory calculations, we show that mono- and bilayer SnP₃ has relatively low cleavage energies of 0.71 and 0.45 J m^–2, lower than several other 2D materials and comparable to that of graphene (0.32 J m^–2). Mono- and bilayer SnP₃ have an indirect band gap of 0.83 and 0.55 eV, respectively, and the magnitude of the gap can be tuned by applying strain. Remarkably, pristine monolayer SnP₃ has a relatively high carrier mobility in the range of 3000–7000 cm² V^–1 s^–1, at par with well-known 2D semiconductors such as MoS₂, phosphorene, and other phosphorus-based layered materials such as GeP₃ and InP₃. Mono- and bilayer SnP₃ also show large optical absorption, resulting from the existence of the van-Hove singularities in the electronic density of states. The combined properties of layered SnP₃, in particular, its high carrier mobility and tunable band gap, along with large optical absorption coefficient, open up interesting possibilities for nanoelectronic and nanophotonic applications

Extreme Optical Anisotropy in the Type-II Dirac Semimetal NiTe₂ for Applications to Nanophotonics

Several bulk transition-metal dichalcogenides exhibit a strong optical anisotropy, high refractive index, and even a natural hyperbolic response, which are enabling ingredients in a variety of nanophotonic scenarios of great interest. Here, we investigate the electromagnetic response of NiTe2, a type-II Dirac semimetal, whose infrared/optical properties have been hitherto largely unexplored. Through density-functional-theory-based ab initio modeling, along with electron energy loss spectroscopy experiments, we show that NiTe2 exhibits a varied, extremely anisotropic response within the infrared and visible ranges. We also demonstrate the high tunability of its optical properties and illustrate the key role played by Dirac fermions. Our results pave the way for realizing nanophotonic devices for efficient light manipulation at subwavelength scales