First-principles Study On The Electronic Structures And Optical Properties Of Non-centrosymmetric Superconductors Y₂C₃、Li₂Pd₃B And Li₂Pt₃B

In this thesis we have used the full-potential local-orbital minimum-basis code FPLO9to study the electronic properties of non-centrosymmetric superconductors including Y2C3, Li2Pd3B and Li2Pt3B and we have also used the full-potential linearized augmented plane wave (FLAPW) code based on density functional theory to study the optical properties of these three compounds. In addition to the usual scalar relativistic effects, we also include the spin-orbital coupling effects on the optical properties of Li2Pd3B and Li2Pt3B.The electronic structures such as the crystal structures, energy band structures, the total density of states figures, the partial wave state density figures, Fermi surface and the relevant optical spectra such as reflectivity R(co), absorbtion, optical conductivity σ(ω) and electron energy loss spectroscopy (EELS) for these three superconducting compounds have been calculated and analyzed. The optical conductivity σ(ω) of Y2C3shows a remarkable Drude-like feature in the low energy region which illustrates the metallic feature of the compound and it’s plasma frequency appears at1.3813eV. While for Li2Pd3B and Li2Pt3B, the σ(ω) spectra exhibit obvious absorption peaks in the low energy region and intensities of σ(ω) decreases gradually with the increase of incident photon energy and their plasma frequency appear at3.0003eV and2.5302eV respectiely. In considering the spin-orbital coupling effect, there appears obvious splitting in the energy bands of Li2Pd3B and Li2Pt3B, and the prominent nodes appear in the energy band of Li2Pt3B, but these impacts on their optical properties is virtually invisible. This research demonstrates that the spin-orbital coupling plays a minor role to the optical properties in these non-centrosymmetric superconductors.