Electronic Structure And Properties Of Hexagonal Lattice From First-Principles Calculations

Since the discovery of the iron-based superconducting materials in2008, transition metal pnictide based superconductors was brought to public interest. Recently, SrPtAs, a transition metal arsenide was discoveried, which exhibits superconducting characteristics at2.4K. Due to the ineligible of spin-orbit coupling and the loss of spacial inversion symmetry, the research about the materials has received wide public interests.To study the physical properties of the materials, we use the first principle numerical simulation based on density functional theory, to study the ABAs (A=of Sr, Ba; B=Pd, Pt) series of compounds. We performed in-depth study over its physical properties, including crystal structures, electronic structures, the SrPtAs phonon spectrum, and the electron-phonon coupling. Calculation shows that band splitting of these materials near Fermi level due to spin-orbit coupling depends strongly on the noble metal elements, with the Pt-based material considerably larger than the Pd-based material. The density of states near Fermi level consists primarily of Pd-4d and Pt-5d orbitals, and the spin-orbit coupling has little influence over the density of states near Fermi level of SrPtAs; while for the high-energy part Ba/Sr’s influence is more obvious. The phonon calculations indicate that the spin-orbit coupling effect has little effect over the phonon spectrum of the material, especially for low-energy phonon. Electron-phonon coupling coefficient was obtained from First principle calculation, and the superconducting transition temperature Tc was estimated to be around2.5K based on BCS theory by using Allen-Dynes equation, which is quite consistent with experimental data. Therefore, the superconducting mechanism in SrPtAs could explain by using electricity phonon coupling, indicating the material is a conventional electron-phonon coupling superconductor.