Orbital characters of bands in the iron-based superconductor BaFe1.85Co0.15As

Abstract

The unconventional superconductivity in the newly discovered iron-based superconductors is intimately related to its multi-band/multi-orbital nature. Here we report the comprehensive orbital characters of the low-energy three-dimensional electronic structure in BaFe1.85Co0.15As2 by studying the polarization and photon energy dependence of angle-resolved photoemission data. While the distributions of the dxz, dyz, and d 3z 2 −r 2 orbitals agree with the prediction of density functional theory, those of the dxy and d x 2 −y 2 orbitals show remarkable disagreement with theory. Our results point out the inadequacy of the existing band structure calculations, and more importantly, provide a foundation for constructing the correct microscopic model of iron pnictides.

The orbital characters of low-energy electronic structure in iron-chalcogenide superconductor K x Fe2−y Se2

“…The band assigned as α only emerges in the p geometry along both #1 and #2 directions, and could not be observed in the s geometry, which indicates its d xz or d z 2 orbital character based on Table 1. The β band shows opposite spatial symmetry, as it could only be observed in the s geometry, thus we attribute it to d yz according to [23]. For the γ band, it emerges in the s geometry along #1 direction, and the p geometry along #2 direction, which is consistent with the symmetry of the d xy orbital.…”

“…Considering the spatial symmetries of the 3d orbitals (Figure 1(b)), when the analyzer slit is along the high-symmetry direction of the sample, the photoemission signal of certain orbitals would appear or disappear by specifying the polarization directions as summarized in Table 1. More detailed information about the polarization-dependent ARPES could be found in [23,28].…”

“…We define the x and y directions to be the two nearest-neighboring Fe-Fe bond directions in Figure 1(c), and the corresponding twodimensional projected Brillouin zone (solid lines) and un- [23]. Table 1 The possibility to detect the 3d orbitals along two high symmetry directions in the p and s geometries, respectively, by polarization-dependent APRES [23] High-symmetry Experimental 3d orbitals…”

“…Polarization-dependent ARPES experiments have been conducted extensively on the iron-based superconductors, including LaOFeAs [13], BaFe 2 As 2 [23][24][25][26][27], NaFeAs [28,29], and FeTe [17,27]. Here we report the polarization-dependent ARPES study on the orbital characters of K x Fe 2−y Se 2 superconductor.…”

s-wave superconductivity with orbital-dependent sign change in checkerboard models of iron-based superconductors

“…The pairing in the d xy orbital favors an opposite sign to those in the d yz and d xz orbitals when J 2 dominates the pairing. This relation, if still holds in the homogeneous limit, will result in the sign change between the hole pockets at Γ which have d yz,xz orbital character and the hole pocket at M in unfolded Brillouin zone which has d xy orbital character 39 , a result can be tested explicitly in future experiments. A schematic plot of this prediction in folded Brillouin zone is shown in Fig.…”