Electronic structure and spin dynamics of ACo2As2 (A=Ba, Sr, Ca)

Abstract

The electronic structures, charge and spin dynamics of the cobalt pnictide compounds ACo2As2 (A=Ba, Sr, Ca) in the paramagnetic state are investigated by using density functional theory combined with dynamical mean-field theory. In contrast to their iron counterparts, these cobalt pnictide compounds have three-dimensional electronic structures and strong ferromagnetic low-energy spin excitations. The Co 3d eg orbitals dominate the electronic states around the Fermi level and have stronger electronic correlation strength than the Co 3d t2g orbitals. The overall electronic correlation strength is much weaker than that in the iron arsenides, however, the most strongly correlated Co 3d x2-y2 orbital, especially in CaCo2As2, has electronic correlation strength comparable to Fe 3d t2g orbitals in iron arsenides. ACo2As2 (A=Ba, Sr, Ca) shows similar electronic structures where a conduction band of primarily Co 3d x2-y2 orbital character is close to a Van Hove singularity around the Brillouin-zone corner, which promotes ferromagnetic low-energy spin excitations. Originated from its increased nearest-neighbor Co-Co distance and significantly reduced As height from the Co plane, the strong electronic correlation strength and close proximity to the Van Hove singularity of the Co 3d x2-y2 orbital in CaCo2As2 is responsible for its unique A-type antiferromagnetic order observed in experiments. In comparison, despite substantial ferromagnetic low-energy spin excitations, BaCo2As2 and SrCo2As2 remain paramagnetic down to very low temperature because the Co 3d x2-y2 orbital has weaker electronic correlation strength and is further away from the Van Hove singularity.

arXiv comment17 pages, 4 figures

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• Flat band magnetism and helical magnetic order in Ni-doped SrCo${}_2$As${}_2$
• Helical magnetic ordering in Sr(Co1-xNix)2As2
• Antiferromagnetic Stacking of Ferromagnetic Layers and Doping Controlled Phase Competition in Ca${}_{1-x}$Sr${}_x$Co${}_{2-y}$As${}_2$
• Competing magnetic fluctuations and orders in a multiorbital model of doped SrCo${}_2$As${}_2$
• A topological Hund nodal line antiferromagnet
• Magnetic order and fluctuations in quasi-two-dimensional planar magnet Sr(Co${}_{1-x}$Ni${}_x$)${}_2$As${}_2$
• Carrier Tuning of Stoner Ferromagnetism in ThCr${}_2$Si${}_2$-Structure Cobalt Arsenides
• Suppression of antiferromagnetic order and strong ferromagnetic spin fluctuations in Ni-doped CaCo2As2 single crystals
• Absence of itinerant ferromagnetism in a cobalt-based oxypnictide
• Weak electronic correlations in the cobalt oxychalcogenide superconductor Na2CoSe2O
• Enhanced Anomalous Nernst Effect in the Ferromagnetic Kondo Lattice CeCo2As2
• Electronic structure of $A$Co${}_2$As${}_2$ ($A=$ Ca, Sr, Ba, Eu) studied using angle-resolved photoemission spectroscopy and theoretical calculations