Geometrical frustration versus Kitaev interactions in BaCo <sub>2</sub> (AsO <sub>4</sub> ) <sub>2</sub>
Thomas Halloran, Félix Desrochers, Emily Z. Zhang, Tong Chen, Li Ern Chern, Zhijun Xu, Barry Winn, M. Graves-Brook, M. B. Stone, А. И. Колесников, Yiming Qiu, Ruidan Zhong, R. J. Cava, Yong Baek Kim, C. Broholm
Abstract
Recently, Co-based honeycomb magnets have been proposed as promising candidate materials to host the Kitaev spin liquid (KSL) state. One of the front-runners is BaCo 2 (AsO 4 ) 2 (BCAO), where it was suggested that the exchange processes between Co 2+ ions via the surrounding edge-sharing oxygen octahedra could give rise to bond-dependent Kitaev interactions. In this work, we present and analyze a comprehensive inelastic neutron scattering (INS) study of BCAO with fields in the honeycomb plane. Combining the constraints from the magnon excitations in the high-field polarized state and the inelastic spin structure factor measured in zero magnetic field, we examine two leading theoretical models: the Kitaev-type <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>JK</mml:mi> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:msup> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:mrow> </mml:math> model and the XXZ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mtext>-</mml:mtext> <mml:msub> <mml:mi>J</mml:mi> <mml:mn>1</mml:mn> </mml:msub> <mml:mtext>-</mml:mtext> <mml:msub> <mml:mi>J</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> model. We show that the existing experimental data can be consistently accounted for by the XXZ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mtext>-</mml:mtext> <mml:msub> <mml:mi>J</mml:mi> <mml:mn>1</mml:mn> </mml:msub> <mml:mtext>-</mml:mtext> <mml:msub> <mml:mi>J</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:mrow> </mml:math> model but not by the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>JK</mml:mi> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:msup> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo>′</mml:mo> </mml:msup> </mml:mrow> </mml:math> model, and we discuss the implications of these results for the realization of a spin liquid phase in BCAO and more generally for the realization of the Kitaev model in cobaltates.