Pressure dependence of structural, elastic, electronic, thermodynamic, and optical properties of van der Waals-type NaSn2P2 pnictide superconductor: Insights from DFT study

Abstract

NaSn2P2 is a recently discovered superconducting system belonging to a particular class of materials with van der Waals (vdW) structure. There is enormous interest in vdW compounds because of their intriguing electrical, optical, chemical, thermal, and superconducting state properties. We have studied the pressure dependent structural, thermo-physical, electronic band structure, and superconducting state properties of this quasi-two dimensional system in details for the first time via ab initio technique. The optical properties are also investigated for different electric field polarizations for the first time. Structural, electronic, and optical properties were explored via density functional theory (DFT) calculations. Thermal properties were investigated using the quasi-harmonic Debye model. NaSn2P2 is found to be mechanically stable in the pressure range 0–3.0 GPa. The elastic anisotropy indices point towards high level of mechanical and bonding anisotropy in NaSn2P2 consistent with its highly layered structure. The elastic constants, moduli, and Debye temperature (θD) show non-monotonic variation with pressure, particularly close to 1.0 GPa. The pressure dependent superconducting transition temperature, Tc, of NaSn2P2 is predicted to vary strongly with the pressure dependent variation of θD. The electronic energy dispersion curves, E(k), reveal high level of direction dependence; the effective masses of charge carries are particularly high for the out-of-plane (c-axis) charge transport. The optical parameters compliment the underlying electronic energy density of states features and are weakly dependent on the polarization of the incident electric field. The reflectivity of NaSn2P2 is very high in the visible region and remains quite high and non-selective over an extended energy range in the ultraviolet region. The absorption coefficient is also high in the mid-ultraviolet band. All these optical features render NaSn2P2 suitable for optoelectronic device applications.