Microscopic Mechanism of a Twisted Kitaev Model

For many years CoNb₂O₆ was believed to be described by the transverse-field Ising model (TFIM). However, recent experimental evidence and symmetry analysis of the crystal structure suggests this compound can be described by variations of the twisted Kitaev model (TKM), which features bond-dependent interactions. Here we study a microscopic mechanism to generate the twisted Kitaev exchange interaction, among others, using a strong-coupling expansion. We combine these results with tight-binding parameters obtained by density-functional theory, and use exact diagonalization to compare the magnetic spectrum of our model with inelastic neutron scattering data.