Anisotropy of the optical conductivity of a pnictide superconductor from the undoped three-orbital Hubbard model

Properties of the multiorbital Hubbard models for the iron-based superconductors

“…The proposed explanation is more elaborated than this simple statement and the readers can find details and additional references in Ref. [113]. Here only a brief summary of the main results is provided.…”

“…Several theoretical publications have been devoted to this topic [111,112]. Members of our group [113] have recently studied the optical conductivity of the three-orbital Hubbard model [74] using mean-field techniques, and indeed observed the presence of an anisotropy, mainly caused by the fact that near the Fermi surface there is an asymmetry in the population of the xz and yz orbitals induced by the magnetic order with wavevector (π, 0) that already breaks rotational invariance [79]. The proposed explanation is more elaborated than this simple statement and the readers can find details and additional references in Ref.…”

Optical conductivity and Raman scattering of iron superconductors

“…We are interested in the response to a homogeneous q = 0 electric field A α q=0 (ω) = E α q=0 (ω)/(iω − δ) with δ a small parameter, and in particular in σ αα (ω), the real part of the optical conductivity, σ αα (ω) = σ αα (ω) + iσ αα (ω) defined as J α q=0 = σ αα (ω)E α q=0 (ω). After some algebra, 36,40 …”

“…It changes sign in some hole-doped samples. 54 Proposals to explain the anisotropy include orbital ordering, 31,34,37 integrated or at the Fermi surface, 36 spin nematicity, 33 anisotropic Fermi velocities, 32 and anisotropic scattering from disorder in the anisotropic magnetic state. 29 Fittings of the Drude peak performed to study whether the anisotropy originates in the Fermi velocities or in the scattering rate are controversial.…”

“…The origin of these anisotropies is not clear yet. 16,21,[25][26][27][28][29][30][31][32][33][34][35][36][37] The Raman spectrum in the magnetic state shows signatures and peaks at energies similar to those found in optical conductivity and it has been interpreted in terms of two kinds of electronic transitions: a high-energy transition between folded anticrossed spin density wave bands and a lower-energy transition which involves a folded and a nonfolded band 7 (see Fig. 1).…”