In the pursuit of novel quantum states arising from entangled spin and orbital degrees of freedom, we report the experimental identification of an emergent vortex lattice in the multiflavor pyrochlore-lattice compound GeCo2O4. This material hosts Co2+ ions in edge-sharing octahedral environments, a geometry known to favor bond-dependent Kitaev interactions. Through comprehensive neutron scattering experiments performed on WISH, 4SEASONS, HIPD, and ZEBRA, we revealed that substantial Kitaev couplings cooperate with geometric frustration to stabilize a unique vortex lattice in this compound.

A cornerstone of this work is the methodological innovation employed to determine the microscopic Hamiltonian, specifically a regularized regression framework based on an effective parameter count. Conventional least-squares fitting in complex frustrated systems often risks overfitting within expanded parameter spaces, making results sensitive to manual selection. To address this, we adapted a two-target fitting approach that balances the goodness-of-fit for inelastic neutron scattering spectra against an effective parameter count defined by a threshold parameter. This analysis generates a Pareto front, allowing for the objective identification of a minimal model that robustly reproduces experimental data while automatically suppressing marginal near-zero coefficients without manual intervention.

More details of our experiments and analyses are presented in arXiv.2605.12042.

(This post is adapted from the output of the Qwen LLM.)