XY magnetism, Kitaev exchange, and long-range frustration in the J(eff)=1/2 honeycomb cobaltates

Article

关键词: GENERALIZED GRADIENT APPROXIMATION;    ELECTRONIC-STRUCTURE;    MODEL;    SIGNATURE;    ORDER;   

DOI  :  10.1103/PhysRevB.104.134425

来源: SCIE

【 摘 要 】

The quest for Kitaev quantum spin liquids has led to great interest in honeycomb quantum magnets with strong spin-orbit coupling. It has been recently proposed that even Mott insulators with 3d transition-metal ions, having nominally weak spin-orbit coupling, can realize such exotic physics. Motivated by this, we study the rhombohedral honeycomb cobaltates CoTiO3, BaCo2(PO4)(2), and BaCo2(AsO4)(2), using ab initio density-functional theory, which takes into account realistic crystal-field distortions and chemical information, in conjunction with exact diagonalization numerics. We show that these Co2+ magnets host J(eff) = 1/2 local moments with highly anisotropicg factors, and we extract their full spin Hamiltonians including longer-range and anisotropic exchange couplings. For CoTiO3, we find a nearest-neighbor easy-plane ferromagnetic XXZ model with additional bond-dependent anisotropies and interlayer exchange, which supports three-dimensional Dirac nodal line magnons. In contrast, for BaCo2(PO4)(2) and BaCo2(AsO4)(2), we find a strongly suppressed interlayer coupling, and significant frustration from additional third-neighbor antiferromagnetic exchange mediated by P or As. Such bond-anisotropic J(1)-J(3) spin models can support collinear zigzag or coplanar spiral ground states. We discuss their dynamical spin correlations which reveal a gapped Goldstone mode and argue that the effective parameters of the pseudospin-1/2 models in these two materials may be strongly renormalized by coupling to a low-energy spin exciton. Our results call for reexamining proposals for realizing Kitaev spin liquids in the honeycomb cobaltates.

【 授权许可】

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