Naher M I, Naqib S H
Department of Physics, University of Rajshahi, Rajshahi, 6205, Bangladesh.
Sci Rep. 2021 Mar 10;11(1):5592. doi: 10.1038/s41598-021-85074-z.
In recent days, study of topological Weyl semimetals have become an active branch of physics and materials science because they led to realization of the Weyl fermions and exhibited protected Fermi arc surface states. Therefore, topological Weyl semimetals TaX (X = P, As) are important electronic systems to investigate both from the point of view of fundamental physics and potential applications. In this work, we have studied the structural, elastic, mechanical, electronic, bonding, acoustic, thermal and optical properties of TaX (X = P, As) in detail via first-principles method using the density functional theory. A comprehensive study of elastic constants and moduli shows that both TaP and TaAs possesses low to medium level of elastic anisotropy (depending on the measure), reasonably good machinability, mixed bonding characteristics with ionic and covalent contributions, brittle nature and relatively high Vickers hardness with a low Debye temperature and melting temperature. The minimum thermal conductivities and anisotropies of TaX (X = P, As) are calculated. Bond population analysis supports the bonding nature as predicted by the elastic parameters. The bulk electronic band structure calculations reveal clear semi-metallic features with quasi-linear energy dispersions in certain sections of the Brillouin zone near the Fermi level. A pseudogap in the electronic energy density of states at the Fermi level separating the bonding and the antibonding states indicates significant electronic stability of tetragonal TaX (X = P, As).The reflectivity spectra show almost non-selective behavior over a wide range of photon energy encompassing visible to mid-ultraviolet regions. High reflectivity over wide spectral range makes TaX suitable as reflecting coating. TaX (X = P, As) are very efficient absorber of ultraviolet radiation. Both the compounds are moderately optically anisotropic owing to the anisotropic nature of the electronic band structure. The refractive indices are very high in the infrared to visible range. All the energy dependent optical parameters show metallic features and are in complete accord with the underlying bulk electronic density of states calculations.
近年来，拓扑外尔半金属的研究已成为物理学和材料科学中一个活跃的分支，因为它们导致了外尔费米子的实现，并展现出受保护的费米弧表面态。因此，从基础物理学和潜在应用的角度来看，拓扑外尔半金属TaX（X = P，As）都是重要的电子系统。在这项工作中，我们使用密度泛函理论通过第一性原理方法详细研究了TaX（X = P，As）的结构、弹性、力学、电子、键合、声学、热学和光学性质。对弹性常数和模量的全面研究表明，TaP和TaAs都具有低到中等水平的弹性各向异性（取决于测量方法）、相当好的可加工性、具有离子和共价贡献的混合键合特性、脆性以及相对较高的维氏硬度，同时德拜温度和熔点较低。计算了TaX（X = P，As）的最小热导率和各向异性。键布居分析支持了弹性参数所预测的键合性质。体电子能带结构计算揭示了在费米能级附近布里渊区的某些部分具有准线性能量色散的清晰半金属特征。费米能级处电子态密度中的赝能隙将成键态和反键态分开，这表明四方TaX（X = P，As）具有显著的电子稳定性。反射光谱在涵盖可见光到中紫外区域的宽光子能量范围内显示出几乎非选择性的行为。宽光谱范围内的高反射率使得TaX适合用作反射涂层。TaX（X = P，As）是非常有效的紫外线辐射吸收剂。由于电子能带结构的各向异性，这两种化合物都具有适度的光学各向异性。在红外到可见光范围内折射率非常高。所有与能量相关的光学参数都显示出金属特征，并且与底层的体电子态密度计算完全一致。
