Figure 2
Leading
dependence of the velocity (optical conductivity) and Raman squared vertices
,
,
, and
defined in Eqs. (
24,
25,
26) for iron superconductors for each pair of orbitals involved in an interband transition in the unfolded 1-Fe Brillouin zone corresponding to the tight-binding model in Ref.
38.
and
directions point along the Fe bonds.
and
are defined in this Brillouin zone and axes. The same assignment is used in the nonmagnetic and the magnetic states. In the case of intraorbital transitions,
probe the electron pockets. Note that a different convention has been used in some Raman articles which define the polarizations according to the tetragonal FeAs Brillouin zone. Darker regions in each figure correspond to larger values of each squared vertex. Combination of optical conductivity and Raman scattering spectroscopy allow us to probe selectively interorbital transitions through the whole Brillouin zone. Intraorbital
squared vertex depends on
as
with the ratio
dependent on the orbital.
valid for
,
, and
has been considered in the figure. The
dependence changes slightly for
,
, but it is maximal in approximately the same regions of the Brillouin zone. The pairs
refer to the product of the parities with respect to
and
reflections for each pair of orbitals (see Sec. 3 for an illustrative example). The vertices for the
transition in
symmetry and for the
transitions in
symmetry vanish. Note that the hoppings between
and
to nearest- and next-nearest-neighbors are zero, so the corresponding vertices cancel within the model considered here. A finite small contribution could arise if hoppings to farther away neighbors were considered.
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