Small anisotropy in iron-based superconductors induced by electron correlation

Abstract

We have investigated the electron correlation effect on the electronic structures and transport properties of the iron-based superconductors using density functional theory (DFT) and dynamical mean field theory (DMFT). By considering the Fe 3d electron correlation using DMFT, the quasiparticle bandwidth near the Fermi level is found to be substantially suppressed compared to the conventional DFT calculation. Because of the different renormalization factors of each 3d orbital, DMFT gives considerably reduced electrical anisotropy compared to DFT results, which explains the unusually small anisotropic resistivity and superconducting property observed in the iron-based superconductors. We suggest that the electron correlation effect should be considered to explain the anisotropic transport properties of the general d/f valence electron system. Discovery of [superconducting transition temperature (T c )] high-T c superconductivity (HTSC) in LaFeAsO 1−x F x with T c = 26 K 1 has stimulated the effort to understand the mechanism of HTSC and search for new materials with this property. Similar to the well-known cuprate superconductors, it has a layered structure with the square lattice of transition metals, and the superconductivity emerges from the boundary of the antiferromagnetic ordering of 3d valence electrons. This indicates that the magnetic ordering, or more likely its fluctuation, is closely related to the electron pairing both in cuprate and iron-based superconductors. Since the first discovery, many subsequent iron-based superconductors have been reported coming from the parent compounds of ReFeAsOF (Re: rare earth elements), AeFe 2 As 2 (Ae: Ba, Sr, and Ca), LiFeAs, FeSe, 2-6 etc. All the superconductors have similar crystal structures and electronic properties. Twodimensional FeAs (or FeSe) layers are commonly observed to be sandwiched by the insulating blocking layers, which induces the anisotropic electronic structures. In all the compounds, multiple Fe 3d orbitals participate in the magnetic or superconducting transitions. Because of the numerous investigations on iron-based superconductors, one could use many available experimental data of their physical properties for the comparative study of these materials in clarifying the origin of HTSC.Anisotropy is an important parameter with which to understand the mechanism of the HTSC. Usually the low dimensionality has been believed to be the crucial factor for increasing the superconducting T c . Most of the compounds with HTSC have layered structure, and the maximum T c among the cuprate superconductors is designed from highly anisotropic compounds. Indeed, density functional theory (DFT) calculations predict two-dimensional electronic structures and anisotropic transport properties of the iron-based superconductors.7 Using the same strategy as that applied to the cuprate superconductors, researchers have tried to synthesize highly anisotropic iron-base superconductors such as Sr 2 VO 3 Fe 2 As 2 with a blocking layer of Sr 2 VO 3 . 6 However, the observed...

Orbital Selective Fermi Surface Shifts and Mechanism of HighTcSuperconductivity in CorrelatedAFeAs(A=Li, Na)

“…Calculated bands have to be renormalized by approximately 2−4 to fit the experimentally measured band width, and the predicted spin magnetic moment is about twice larger than the experimental value. On the other hand, the dynamical mean field theory (DMFT) on top of the DFT showed consistent results with the measured bands, the anisotropy and the small magnetic moment [16][17][18][19][20][21].…”

“…On the other hand, the dynamical mean field theory (DMFT) on top of the DFT showed consistent results with the measured bands, the anisotropy and the small magnetic moment. [11][12][13][14][15][16] Even though DMFT has been shown to work well, the comparison of calculated and measured band structures, especially the FS, is still important to check the validity of the calculation. For an accurate comparison of theory and experiment, LiFeAs is the most suitable system at present.…”

Atomically imaged crystal structure and normal-state properties of superconducting Ca10Pt4As8Wang1, Jin2, Tao3 et al. 2019Phys. Rev. B4110View full textAdd to dashboardCite

“…5(b). The large ρ c /ρ ab makes Ca 10 Pt 4 As 8 ((Fe 1-x Pt x ) 2 As 2 ) 5 one of the most anisotropic materials in the class of Fe-based superconductors [30][31]. The large anisotropy is most likely a result of directional disorder as discussed in Ref.…”

Electrical and Thermal Transport Properties of Layered Superconducting Ca10(Pt4As8)((Fe0.86Pt0.14)2As2)5 Single Crystal

“…The resistivity anisotropy γ is calculated by γ=ρc/ρab and it increases from ~4.1 at 300 K to ~7.9 around T c as displayed in Figure 5. The γ of Ca 10 Pt 4 As 8 (Fe 2 As 2 ) 5 is larger than that of LaFeAsO 0.9 F 0.1 [17]. Relatively large anisotropy and a conspicuous difference in the behavior of ρ c and ρ ab suggests rgw strong 2D nature of electronic structures in Ca 10 Pt 4 As 8 (Fe 2 As 2 ) 5 , which is rarely encountered in traditional Fe-based superconductors.…”