Non-local correlations in Iron Pnictides and Chalcogenides

Abstract

Deviations of low-energy electronic structure of iron-based superconductors from density functional theory predictions have been parametrized in terms of band-and orbital-dependent mass renormalizations and energy shifts. The former have typically been described in terms of a local self-energy within the framework of dynamical mean field theory, while the latter appears to require non-local effects due to interband scattering. By calculating the renormalized bandstructure in both random phase approximation (RPA) and the two-particle self-consistent approximation (TPSC), we show that correlations in pnictide systems like LaFeAsO and LiFeAs can be described rather well by a non-local self-energy. In particular, Fermi pocket shrinkage as seen in experiment occurs due to repulsive interband finite-energy scattering. For the canonical iron chalcogenide system FeSe in its bulk tetragonal phase, the situation is however more complex since even including momentum-dependent band renormalizations cannot explain experimental findings. We propose that the long-range Coulomb interaction may play an important role in band-structure renormalization in FeSe. We further compare our evaluations of non-local quasiparticle scattering lifetime within RPA and TPSC with experimental data for LiFeAs.

Anisotropy of electronic correlations: On the applicability of local theories to layered materials

“…1. Concurringly, diagrammatic fluctuation techniques recently demonstrated 92,93 that static non-local renormalizations are indeed nonnegligible-in line with previous experimental analyses 94 . Non-local corrections to dynamical renormalizations, however, were previously shown 95 to be small, at least away from the systems' Néel temperatures.…”

On the Spatial Locality of Electronic Correlations in LiFeAs

“…This strong momentum dependence of the dynamical self-energy of the xz/yz orbitals has been discussed in Refs. [5,6,18,24] in relation to the strong coupling of the quasiparticles of the xz/yz driven α and α ′ hole-like FS sheets to the existing AFM correlation in LiFeAs [48]. Indeed, these FS sheets are close to the AFM zone boundary.…”

“…This has been addressed previously by a comparison of theoretical calculations to experiments. Some results favor the local picture [13][14][15][16][17][18][19][20][21] while others support the non local view [5,6,[22][23][24].…”

Linkage between scattering rates and superconductivity in doped ferropnictides

“…They obtained a quadratic-in-energy dependence of the scattering rates Γ(E, T ≈ 0) corresponding to a Fermi liquid behavior. Moreover, combined density functional plus dynamical mean field theory (DFT+DMFT) calculations derive by construction a quadratic energy dependence of Γ(E, T ) [5,7,10,11].…”

“…Recently, there were several combined density functional/dynamical mean-field theory (DFT + DMFT) calculations on the scattering rates in FeSCs [5,7] and calculation also taking non-local effects into account [10,11]. Inherent to DFT+DMFT calculations, the calculated scattering rates always showed a Fermi liquid behavior, except one calculation which presented a linear in energy dependence down to the lowest energies [10].…”