Observation of the Dirac Dispersions in Co-doped CaFe2As2

TL;DR

This study uses ARPES to explore the electronic structure of CaFe2As2 and Co-doped variants, revealing Dirac cones and changes across magnetic and superconducting phases, advancing understanding of iron pnictide superconductors.

Contribution

First ARPES investigation of Dirac dispersions in CaFe2As2 and Co-doped variants across different phases, linking electronic structure features to magnetic and superconducting states.

Findings

Dirac cones found at 30 meV below Fermi energy in SDW phases

Electronic structure evolves with cobalt doping from SDW to superconducting phases

Characteristic features of antiferromagnetic and paramagnetic phases identified

Abstract

We performed an angle-resolved photoemission spectroscopy (ARPES) study of the electronic structure of the CaFe$_2$As$_2$ 122-iron pnictide, a parent compound, and two iron-based superconductors CaFe$_{2-x}$Co$_x$As$_2$ ($x = 0.07$ 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 the samples with 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 Fermi energy for nonsuperconducting CaFe$_2$As$_2$ and superconducting CaFe$_{1.93}$Co$_{0.07}$As$_2$ orthorhombic SDW systems.