<i>Ab initio</i> guided minimal model for the “Kitaev” material <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">BaCo</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi mathvariant="normal">AsO</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>: Importance of direct hopping, third-neighbor exchange, and quantum fluctuations
P. A. Maksimov, Alexey V. Ushakov, Z. V. Pchelkina, Ying Li, Stephen M. Winter, S. V. Streltsov
Abstract
By considering two ab initio-based complementary approaches, we analyze the electronic structure and extract effective spin models of ${\mathrm{BaCo}}_{2}{({\mathrm{AsO}}_{4})}_{2}$, 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 ${\mathrm{BaCo}}_{2}{({\mathrm{AsO}}_{4})}_{2}$. Remarkably, it is the third-neighbor interactions, both isotropic and anisotropic, that are responsible for the standout double-zigzag ground state of ${\mathrm{BaCo}}_{2}{({\mathrm{AsO}}_{4})}_{2}$, 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 ${\mathrm{BaCo}}_{2}{({\mathrm{AsO}}_{4})}_{2}$.