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First-principles Study on Electronic Structures and Hyperfine Interactions of Iron-based Superconductor

Author: FangYang
Tutor: PangHua
School: Lanzhou University
Course: Condensed Matter Physics
Keywords: First-principles calculations Iron-based superconductors Hyperfine parameters Electronic structure Fermi
CLC: O511
Type: Master's thesis
Year: 2011
Downloads: 104
Quote: 0
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Abstract


Based on first-principles density functional theory, with the full-potential linearized augmented plane wave method for iron-based superconductors BaFe2As2, SrFeAsF maternal and K1-yFe2-xSe2 electronic structure and hyperfine parameters (electric field gradients, hyperfine field and homogeneity abilities shift) were studied. First, we examine the LDA (GGA) (?) Method under low temperature antiferromagnetic phase BaFe2As2 orthogonal matrix hyperfine parameters. In GGA U (LDA U) exchange-correlation, the placeholder will be a negative Coulomb interaction added to Fe-3d (?) States that when U =-0.1Ry (-0.08 Ry) when, Fe-bit moments and hyperfine parameters calculated in good agreement with the experimental values, but caused by the negative U electronic structure can not reproduce the experimentally measured Fermi surface, especially certain details of the Fermi surface. This indicates that the negative U just coincidence hyperfine parameters and experimental values ??of the magnetic moment, it did not improve the density functional theory electronic structure of iron-based superconducting description. The results show that the precursor antiferromagnetic BaFe2As2, their magnetic properties, structure and there is a strong electronic coupling between the electric field gradient near the Fermi level is closely related to the electronic structure. GGA exchange-correlation matrix under SrFeAsF electronic structure and the electric field gradient calculations show that the architecture phase transition on the electronic structure SrFeAsF maternal influence is very small, and when the system of the magnetic phase transition occurs when the electron distribution has greatly reorganization, indicating that maternal SrFeAsF there is a strong electron - spin interaction. Vzz calculations show, Vzz mainly from the Fermi energy near Fe-3d electron contribution. Magnetic phase transition density of states at the Fermi energy varies greatly, N (EF) becomes small. From the topology of the Fermi level can be seen, the magnetic phase transition SrFeAsF precursor carrier density decreased significantly, only a small amount of hole conduction, which may be observed in the positive experiment Hall coefficient correlation. Finally, also in the GGA exchange-correlation functionals, we are on the K1-yFe2-xSe2 electronic structure and hyperfine parameters were calculated. And KFe2Se2 different, K1-yFe2-xSe2 system at the Fermi energy density value N (EF) Apart from the dxy and dxz yz orbital contributions, and dz2 orbital contributions. From the antiferromagnetic state density of states shows, K1-yFe2-xSe2 system instability at the edge of the spin. K1-yFe2-xSe2 system Fe-bit field gradient and hyperfine field isomorphic BaFe2As2 than their larger system, system characteristics change valence electrons almost no effect on the IS. The electric field gradient with ENERGY CHANGE analysis shows, K1-yFe2-xSe2 system and BaFe2As2 and SrFeAsF system has a significantly different, namely EFG mainly from 0.2 eV below the Fermi level within the energy range of electron spatial distribution anisotropy contributions. It can be speculated, K-bit hole doping might be KxFe2Se2 system at the Fermi energy has great influence on the electronic properties, thereby affecting the system superconductivity.

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CLC: > Mathematical sciences and chemical > Physics > Low Temperature Physics > Superconductivity
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