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Register a new userElectronic band structure, Fermi surface and effect of spin-orbit coupling for tetragonal low-temperature superconductor Bi2Pd from first principles
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We have examined theoretically the electronic band structure and Fermi surface of tetragonal low-temperature superconductor Bi2Pd. Our main results are that (i) the Pd 4d and Bi 6p states determine the main peculiarities of the multiple-sheets FS topology, thus for this material the complicated superconducting gap structure with different energy gaps on different FS sheets should be assumed; (ii) the effect of the spin-orbit coupling is of minor importance for the distributions of the near-Fermi electronic states; and (iii) this phase adopts 3D-like type owing to the directional bonds between the adjacent atomic sheets.
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Based on First-principles calculation, we have investigated electronic structure of a ZrCuSiAs structured superconductor LaNiPO. The density of states, band structures and Fermi surfaces have been given in detail. Our results indicate that the bonding of the La-O and Ni-P is strongly covalent whereas binding property between the LaO and NiP blocks is mostly ionic. Its also found that four bands are across the Fermi level and the corresponding Fermi surfaces all have a two-dimensional character. In addition, we also give the band decomposed charge density, which suggests that orbital components of Fermi surfaces are more complicated than cuprate superconductors.
By means of the first-principles calculations, we have studied in details the structural, elastic and electronic properties of the new tetragonal CaBe2Ge2-type 5.2K superconductor SrPt2As2 in comparison with two hypothetical SrPt2As2 polymorphs with ThCr2Si2-type structures which differ by atomic configurations of [Pt2As2] (or [Pt2As2]) blocks. We have found that CaBe2Ge2-type SrPt2As2 is a quite unique system with complicated 2D-3D character of near-Fermi bands, and the intermediate type of the Fermi surface, which consists of electronic pockets having cylinder-like (2D) topology (typical for 122 FeAs phases) together with 3D-like electronic and hole pockets, which are characteristic for ThCr2Si2-like iron-free low-Tc superconductors. Our analysis reveals that against ThCr2Si2-like 122 phases, the other features for CaBe2Ge2-like SrPt2As2 are: (1). The essential differences of contributions of states from [Pt2As2] and [Pt2As2] blocks into near-Fermi region when the conduction is expected to be anisotropic and happening mainly in [Pt2As2] blocks; (2). The formation of the 3D system of strong covalent Pt-As bonds (inside and between of [Pt2As2]/[As2Pt2] blocks) which is responsible for enhanced stability of this polymorph, and (3). the essential charge anisotropy between the adjacent [Pt2As2] and [As2Pt2] blocks. We have predicted also that CaBe2Ge2-like SrPt2As2 is mechanically stable, relatively soft material with high compressibility and will behave in a ductile manner. On the contrary the ThCr2Si2-type SrPt2As2 polymorphs which contain only [Pt2As2] or [As2Pt2] blocks, are less stable, their Fermi surfaces adopt a multi-sheet three-dimensional type - similar to ThCr2Si2-like iron-free 122 phases, and these polymorphs will be ductile materials with high elastic anisotropy.
Very recently, as an important step in the development of layered Fe-free pnictide-oxide superconductors, the new phase BaTi2Bi2O was discovered which has the highest TC (about 4.6 K) among all related non-doped systems. In this Letter, we report for the first time the electronic bands, Fermi surface topology, total and partial densities of electronic states for BaTi2Bi2O obtained by means of the first-principles FLAPW-GGA calculations. The inter-atomic bonding picture is described as a high-anisotropic mixture of metallic, covalent, and ionic contributions. Besides, the structural and electronic factors, which can be responsible for the increased transition temperature for BaTi2Bi2O (as compared with related pnictide-oxides BaTi2As2O and BaTi2Sb2O), are discussed.
By means of first-principles calculations? we have probed the peculiarities of the elecrtonic band structure and Fermi surface for the recently discovered layered superconductor LaO0.5F0.5BiSi2 in comparison with the parent phase LaOBiO2. The electronic factors prpmoting the transition of LaOBiS2 upon fluorine doping to superconducting state: inter-layer charge transfer, the evolution of the Fermi surface, and the dependence of the near-Fermi densities of states on x for LaO1-xFxBiS2 are evaluated and discussed in comparison with the available experiments.
The (Ca,R)FeAs2 (R=La,Pr and etc.) superconductors with a signature of superconductivity transition above 40 K possess a new kind of block layers that consist of zig-zag As chains. In this paper, we report the electronic structure of the new (Ca,La)FeAs2 superconductor investigated by both band structure calculations and high resolution angle-resolved photoemission spectroscopy measurements. Band structure calculations indicate that there are four hole-like bands around the zone center $Gamma$(0,0) and two electron-like bands near the zone corner M(pi,pi) in CaFeAs2. In our angle-resolved photoemission measurements on (Ca0.9La0.1})FeAs2, we have observed three hole-like bands around the Gamma point and one electron-like Fermi surface near the M(pi,pi) point. These results provide important information to compare and contrast with the electronic structure of other iron-based compounds in understanding the superconductivity mechanism in the iron-based superconductors.
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