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تسجيل مستخدم جديدSignificant contribution of As 4p orbitals to the low-lying electronic structure of 112-type iron-based superconductor Ca0.9La0.1FeAs2
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We report a systematic polarization-dependent angle-resolved photoemission spectroscopy study of the three-dimensional electronic structure of the recently discovered 112-type iron-based superconductor Ca1-xLaxFeAs2 (x = 0.1). Besides the commonly reported three hole-like and two electron-like bands in iron-based superconductors, we resolve one additional hole-like band around the zone center and one more fast-dispersing band near the X point in the vicinity of Fermi level. By tuning the polarization and the energy of incident photons,we are able to identify the specific orbital characters and the kz dependence of all bands. Combining with band calculations, we find As 4pz and 4px (4py) orbitals contribute significantly to the additional three-dimensional hole-like band and the narrow band, respectively. Also, there are considerable hybridization between the As 4p zand Fe 3d orbitals in the additional hole-like band, which suggests the strong coupling between the unique arsenic zigzag bond layers and the FeAs layers therein. Our findings provide a comprehensive picture of the orbital characters of the low-lying band structure of 112-type iron-based superconductors, which can be a starting point for the further understanding of their unconventional superconductivity.
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CaFeAs2 is a parent compound of recently discovered 112-type iron-based superconductors. It is predicted to be a staggered intercalation compound that naturally integrates both quantum spin Hall insulating and superconducting layers and an ideal syst
em for the realization of Majorana modes. We performed a systematical angle-resolved photoemission spectroscopy and first-principle calculation study of the slightly electron-doped CaFeAs2. We found that the zigzag As chain of 112-type iron-based superconductors play a considerable role in the low-energy electronic structure, resulting in the characteristic Dirac-cone like band dispersion as the prediction. Our experimental results further confirm that these Dirac cones only exists around the X but not Y points in the Brillouin zone, breaking the S4 symmetry at iron sites. Our findings present the compelling support to the theoretical prediction that the 112-type iron-based superconductors might host the topological nontrivial edge states. The slightly electron doped CaFeAs2 would provide us a unique opportunity to realize and explore Majorana fermion physics.
We use inelastic neutron scattering to study the low-energy spin excitations of 112-type iron pnictide Ca$_{0.82}$La$_{0.18}$Fe$_{0.96}$Ni$_{0.04}$As$_{2}$ with bulk superconductivity below $T_c=22$ K. A two-dimensional spin resonance mode is found a
round $E=$ 11 meV, where the resonance energy is almost temperature independent and linearly scales with $T_c$ along with other iron-based superconductors. Polarized neutron analysis reveals the resonance is nearly isotropic in spin space without any $L$ modulations. Due to the unique monoclinic structure with additional zigzag arsenic chains, the As $4p$ orbitals contribute to a three-dimensional hole pocket around $Gamma$ point and an extra electron pocket at $X$ point. Our results suggest that the energy and momentum distribution of spin resonance does not directly response to the $k_z$ dependence of fermiology, and the spin resonance intrinsically is a spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of weak spin-orbital coupling.
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