Ab initio guided minimal model for the "Kitaev" material BaCo2(AsO4)2: Importance of direct hopping, third-neighbor exchange, and quantum fluctuations

By considering two ab initio-based complementary approaches, we analyze the electronic structure and extract effective spin models of BaCo2(AsO4)2, a honeycomb material which has been proposed as a candidate for Kitaev physics. Both methods show that the dominant direct hopping makes the bond-dependent Kitaev term negligible, diverting the material away from the sought-after spin-liquid regime. As a result, we present a simple three-parameter exchange model to describe the interactions of the lowest doublet of the honeycomb cobaltate BaCo2(AsO4)2. Remarkably, it is the third-neighbor interactions, both isotropic and anisotropic, that are responsible for the standout double-zigzag ground state of BaCo2(AsO4)2, stabilized by quantum fluctuations. A significantly large third-nearest-neighbor hopping, observed ab initio, supports the importance of the third-neighbor interactions in the stabilization of the unique ground state of BaCo2(AsO4)2.