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arXiv 1809.08550cond-mat.str-el
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ACo2As2(A=Ba,Sr,Ca)的电子结构和自旋动力学

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

Huican Mao, Zhiping Yin

摘要:

采用密度泛函理论结合动力学平均场论理论,研究了钴磷属元素化合物ACo 2As 2(A=Ba,Sr,Ca)顺磁态的电子结构、电荷和自旋动力学.与它们的铁对应物相比,这些钴磷属化合物具有三维电子结构和强铁磁低能自旋激发。Co的3d eg轨道在费米能级附近占据主导地位,并且具有比Co的3d t2 g轨道更强的电子关联强度。整体的电子关联强度比铁砷化物弱得多,然而,最强关联的Co 3d x2-y2轨道,特别是在CaCo 2As 2中,具有与铁砷化物中的Fe 3d t2 g轨道相当的电子关联强度。ACo_2As_2(A=Ba,Sr,Ca)具有相似的电子结构,其导带主要为Co 3d x_2-y_2轨道,在布里渊区拐角处接近Van Hove奇点,这促进了铁磁低能自旋激发。CaCo_2As_2中Co_3dx_2-y_2轨道的强电子关联强度和与Van Hove奇点的紧密接近是导致其独特的A型反铁磁有序的原因,这是由于其最近邻Co-Co距离的增加和As离Co面高度的显著降低.相比之下,尽管大量的铁磁低能自旋激发,BaCo 2As 2和SrCo 2As 2保持顺磁性下降到非常低的温度,因为Co 3d x2-y2轨道具有较弱的电子相关强度,并进一步远离范霍夫奇点。

英文摘要:

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.

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