Electronic structure of $A$Co${}_2$As${}_2$ ($A=$ Ca, Sr, Ba, Eu) studied using angle-resolved photoemission spectroscopy and theoretical calculations

Abstract

We present a comprehensive study of the low-energy band structure and Fermi surface (FS) topology of $A$Co${}_2$As${}_2$ ($A=$ Ca, Sr, Ba, Eu) using high-resolution angle-resolved photoemission spectroscopy. The experimental FS topology and band dispersion data are compared with theoretical full-potential linearized augmented-plane-wave (FP-LAPW) calculations, which yielded reasonably good agreement. We demonstrate that the FS maps of $A$Co${}_2$As${}_2$ are significantly different from those of the parent compounds of Fe-based high-temperature superconductors. Further, the FSs of CaCo${}_2$As${}_2$ do not show significant changes across its antiferromagnetic transition temperature. The band dispersions extracted in different momentum $(k_x,k_y)$ directions show a small electron pocket at the center and a large electron pocket at the corner of the Brillouin zone (BZ). The absence of the hole FS in these compounds does not allow nesting between pockets at the Fermi energy ({\it E}${}_{\mathrm{F}}$), which is in contrast to $A$Fe${}_2$As${}_2$-type parent compounds of the iron-based superconductors. Interestingly, we find that the hole bands are moved 300--400~meV below $E_{\mathrm{F}}$ depending on the $A$ element. Moreover, the existence of nearly flat bands in the vicinity of $E_{\mathrm{F}}$ are consistent with the large density of states at $E_{\mathrm{F}}$. These results are important to understand the physical properties as well as the possibility of the emergence of superconductivity in related materials.

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