Observation of the Dirac Dispersions in Co-Doped CaFe2As2

We performed an angle-resolved photoemission spectroscopy (ARPES) study of the electronic structure of the CaFe2As2 122-iron pnictide, a parent compound, and two iron-based superconductors CaFe2-x Co x As2 (x = 0.07 and 0.15). We studied the band structure of this system across the phase diagram with the transition from the orthorhombic spin density wave (SDW) phase to the tetragonal paramagnetic phase. We observed characteristic features of the electronic structures corresponding to the antiferromagnetic phase in the parent compound and in the samples with a low cobalt concentration (x = 0.07). For highly doped systems (x = 0.15), the measurements revealed the concentric branches of the Fermi surface, which are associated with paramagnetic and superconducting 122-iron pnictides. We found the existence of Dirac cones located at 30 meV below the Fermi energy for nonsuperconducting CaFe2As2 and superconducting CaFe1.93Co0.07As2 orthorhombic SDW systems.