Electronic, optical, and thermoelectric characteristics of (Ae)xFBiS2 (Ae=Sr, Ba, and x=1.7) layered materials useful in optical modulator devices

Abstract

The recent discovery of superconductivity behavior in the mother BiS₂-layered compounds has captivated the attention of several physicists. The crystal structure of superconductors with alternate layers of BiS₂ is homologous to that of cuprates and Fe-based superconductors. The full-potential linearized augmented plane-wave (FP-LAPW) technique was utilized to investigate the electronic structures and density of states in the vicinity of the Fermi energy of SrFBiS₂ and BaFBiS₂ compounds under the electron carriers doping. The introduction of electron doping (carries doping) reveals that the host compounds SrFBiS₂ and BaFBiS₂ exhibit features indicative of superconductivity. This carrier doping of SrFBiS₂ and BaFBiS₂ compounds (electron-doped) has a significant impact on the lowest conduction states near the Fermi level for the emergence of the superconducting aspect. The electron doping modifies and induces changes in the electronic structures with superconducting behavior in (Ae)_1.7FBiS₂(Ae=Sr,Ba) compounds. A Fermi surface nesting occurred under the modification of electrons (carriers) doping in the host compounds SrFBiS₂ and BaFBiS₂. Furthermore, the optical characteristics of the carrier-doped SrFBiS₂ and BaFBiS₂ compounds are simulated. Due to the anisotropic behavior, the optical properties of these materials based on BiS₂ demonstrate a pronounced polarization dependency. The starting point at zero photon energy in the infrared region is elucidated by considering the Drude features in the optical conductivity spectra of SrFBiS₂ and BaFBiS₂ compounds, when the electron carriers doping is applied. It was clearly noticed that the spin-orbit coupling (SOC) influences the electronic band structures, density of states, Femi surface, and optical features because of the heavy Bismuth atom, which may disclose fascinating aspects. Further, we conducted simulations to assess the thermoelectric properties of these mother compounds. The two BiS₂-layered compounds could be suitable for practical thermoelectric purposes and are highlighted through assessment of electrical conductivity, thermal conductivity, Seebeck coefficient, and power factor. As a result, we propose that the mechanisms of superconducting behavior in BiS₂ family may pave new avenues for investigating the field of unconventional superconductivity. It may also provide new insights into the origin of high-T_c superconductivity nature.

Keywords: Drude model; Electronic band structure; Fermi surface nesting; Optical anisotropy; Optical modulators; Thermoelectric.