Guangtao Wang

Electronic structure and magnetism of ThFeAsN

The electronic structure and magnetic properties of ThFeAsN, a newly discovered superconductor, are investigated by means of first-principles calculations. ThFeAsN shares electronic structure and magnetic properties similar to those of LaOFeAs. Its calculated ground state is the stripe antiferromagnetic state. The hole-like Fermi surfaces (FSs) along the line largely overlap with the electron-like FS along the line with the vector . Such significant FS nesting induces a peak of the bare susceptibility at the M-point.

Self-hole-doping–induced superconductivity in KCa2Fe4As4F2

The electronic structure, magnetism, Fermi surface nesting, and bare susceptibility of the superconductor KCa2Fe4As4F2 are discussed in relation to the Fe-pnictide superconductors based on the first-principle calculations. There are ten bands crossing the Fermi level in the nonmagnetic (NM) states, resulting in six hole-like Fermi surface (FS) sheets along the line and four electron-like FS sheets along the line. It is more complicated than other FeAs-based superconductors, showing multi-bands character. Fixed spin moment calculations and the total energies of different magnetic phase indicate that KCa2Fe4As4F2 has a strong tendency towards magnetism, i.e., the stripe antiferromagnetic state. But the self-hole-doping suppressed the spin-density wave state, and then induced superconductivity in the parent compound. Such self-doping strategy may be used for future exploration of new superconductors.

The electronic structure of LaCo2B2

The electronic structure of the recently discovered LaCo2B2 was studied from first-principles calculations. Our results indicate that the hybridization between Co-3d and B-2p is much stronger than that between Fe-3d and As-4p in LaOFeAs and BaFe2As2, which removes the magnetic ordering of Co ions. Therefore, the ground state of LaCo2B2 is nonmagnetic. At the Fermi level, the density of state of La-5d is very high and here are four bands cutting across the Fermi level, which are mostly derived from dz2−3r2 and dyz/zx orbitals. Such results are different with both LaOFeAs and BaFe2As2. The substitution of La by Y atoms would not change the ground state, while substitution of La with Sc atoms might induce a magnetic moment on the Co atom. Comparing with LuNi2B2C2, we classify LaCo2B2 as a BCS superconductor.