Understanding the magnetic interactions of the zig-zag honeycomb lattice: Application to $α$-RuCl$_3$

Abstract: This investigation covers the effects of variable exchange interactions on the spin dynamics of the zig-zag honeycomb lattice. Using a Holstein-Primakoff expansion of the Heisenberg Hamiltonian with easy-axis anisotropy, we characterize the effects of multiple nearest-neighbor and next-nearest-neighbor interactions with asymmetry within the context of a frustrated and non-frustrated zig-zag magnetic configuration. Furthermore, we compare to the known inelastic neutron scattering data for the proximate quantum spin liquid $\alpha$-RuCl$_3$, and we provide insight into the evolution of the spin dynamics, showing that the Heisenberg interaction dominates the majority of the spin excitation behavior. By analyzing the frustrated system with multiple interactions, direction-dependent Dirac nodes present themselves, and we can demonstrate that a standard Heisenberg model can accurately describe the observed magnon spectra.