Effects of Disordered Ru Substitution in ${\mathrm{BaFe}}_2{\mathrm{As}}_2$: Possible Realization of Superdiffusion in Real Materials

An unexpected insensitivity of the Fermi surface to impurity scattering is found in Ru substituted ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ from first-principles theory, offering a natural explanation of the unusual resilience of transport and superconductivity to a high level of disordered substitution in this material. This robustness is shown to originate from a coherent interference of correlated on-site and intersite impurity scattering, similar in spirit to the microscopic mechanism of superdiffusion in one dimension. Our result also demonstrates a strong substitution dependence of the Fermi surface and carrier concentration and provides a resolution to current discrepancies in recent photoelectron spectroscopy. These effects offer a natural explanation of the diminishing long-range magnetic, orbital, and superconducting orders with high substitution.

Figure 1

The lattice constants (Å) [13, 29, 30], band structure (the top panel), low energy band structure (the second panel), the Fermi surface around the $\Gamma$ point with $k_z=0$ (the third panel), and the Fermi surface around the $Z$ point with $k_z=2\pi /c$ (the bottom panel) for $\mathrm{Ba}({\mathrm{Fe}}_{1-x}{\mathrm{Ru}}_x{)}_2{\mathrm{As}}_2$ with different Ru concentrations $x=0$ (a), 0.21 (b), 0.38 (c), 0.55 (d), 0.75 (e), and 1.0 (f). The orbital characters of Fe, Ru, and As are distinguished by the colors given in the legends. The resulting carrier density per Fe and density of states at the Fermi level $N(E_F)$ per (eV Fe) are given below the plots.

Figure 2

(a) Spectral function and (b) band structure for a system with two types of disorder, (c) with only the diagonal disorder and (d) with only the off-diagonal disorder for disordered $\mathrm{Ba}({\mathrm{Fe}}_{0.62}{\mathrm{Ru}}_{0.38}{)}_2{\mathrm{As}}_2$. (e) Single-impurity induced coupling between the Bloch orbitals near and far from the chemical potential, indicated by the red (upper) and black (lower) segments in (d).

Figure 3

Comparison of the Fermi surface at the $k_z=2\pi /c$ plane between the ARPES results [15] (top panel) and our results (bottom panel) in the 1-Fe zone for different Ru concentrations $x=0.02$ (a), 0.21 (b), 0.36 (c), and 0.55 (d). The dashed lines mark the true 2-Fe Brillouin zone boundaries.