Department of Magnetic Reseach Seminar
Microsoft Teams
Ab-initio study of electronic structure of FeAs-based superconductors
mgr Thi Ly Mai
Oddział Badań Magnetyków INTiBS PAN we Wrocławiu
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Streszczenie:
We applied two Ab-initio methods: FP-LAPW and PP-PAW to investigate the electronic properties of several FeAs-based superconductors. Our work has been carried out with the aim of determining the magnetic stability and possible mechanism responsible for the high-Tc superconductivity in SrAFe4As4 (A = Rb, Cs) [1], CaAFe4As4 (K, Rb, Cs) (denoted as 1144) [2], and Sr4V2O6Fe2As2 materials [3, 4, 5]. Thus, the electronic properties, including Densities of States (DOS), Electronic Bands (EB), Fermi Surface (FS), and Electron Localization Function (ELF) of the above-mentioned materials and also their parents (Sr, Ca, A)Fe2As2 (denoted as 122) have been established. In addition, we have appraised the optical and phonon properties of SrRbFe4As4 [6]. The obtained data may be categorized into three topics: i) Possible mechanism of high-Tc superconductivity in 1144: First of all, our calculated data have indicated the non-magnetic state of the Fe ions in (Sr, Ca)AFe4As4. A comparison of the electronic properties between 1144 and 122 divulges stronger inter-band scattering but the weakness of covalent bonds in the first series of compounds. This finding has been proposed as a crucial factor in
entrenching the high-Tc superconductivity. Furthermore, amongst the studied 1144 superconductors, only SrRbFe4As4 and CaCsFe4As4 exhibit unusual FS, which are reminiscent of those in a nodal d-wave gap superconductor, thus these materials may provide a fascinating glimpse into the relationship between high-Tc superconductivity and unconventional mechanism. ii) The coexistence of magnetism and superconductivity in Sr4V2O6Fe2As2: Investigations of magnetic stability in Sr4V2O6Fe2As2 have predicted the most stable state with the AF (q2 = 0.125, 0.125, 0) ordering of V atoms (1.25 µB/V) regarding an incommensurate AF (q1 = 0, 0, 0.306) and the non-magnetic ones. In a similar manner to the 1144 vs 122 materials, the AF Sr4V2O6Fe2As2 phases exhibit higher numbers of electronic bands crossing EF than those in NM state. This suggests stronger inter-band scattering in the magnetic one. These features actually point out the coexistence of magnetism and superconductivity in Sr4V2O6Fe2As2. Remarkably, the Dirac-cone-like structure with a small gap was found between the bands in the vicinity to EF. Interestingly enough, the Fermi velocities manifest a highly anisotropic distribution of electrons that give rises to both horizontal and vertical nodal lines in this superconductor. iii) The optical and phonon properties of SrRbFe4As4. On the whole, the optical parameters display an anisotropic behavior and strong responses to the infrared and visible lights, being due to the intra-band and inter-band transition of Fe-3d and As-4p. The phonon dispersion with no imaginary part conveys the dynamical stability, whereas the phonon density of states discloses strong vibrations of Fe and As atoms. Moreover, a large electron-phonon coupling and the phonon anomaly imply the strong coupling in this superconductor.
References
[1] T. L. Mai and V. H. Tran, Computational Material Science, 156 (2019), 206 - 214.
[2] T. L. Mai and V. H. Tran, Computational Material Science, 169 (2019), 109 - 114.
[3] T. L. Mai and V. H. Tran, Computational Material Science, 179 (2020), 109 - 676.
[4] T. L. Mai and V. H. Tran, Materials Transactions, 61 (2020), 1445 - 1448.
[5] T. L. Mai and V. H. Tran, Acta Physica Polonica A, 138 (2020), 740 - 743.
[6] T. L. Mai and V. H. Tran, Materials Today Communications, under review.
