BaCo₂(AsO₄)₂: Strong Kitaev, After All

BaCo₂(AsO₄)₂—a magnetic compound first studied by one of the present authors 50 years ago—has long been a mystery. Its spectrum is incompatible with the theory that this material was supposed to verify, and its magnetic order is discrepant and easily destroyed by an exceptionally low magnetic field. All these traits have perplexed theorists and experimentalists alike. The mystery had to wait for breakthroughs such as the development of the novel concept of "Kitaev magnetism" in the late 2000s. It had to wait even longer as the first, more obvious Kitaev candidates were studied, before researchers turned their attention to the cobaltate family. Only recently did the stars align to enable a comprehensive analysis of this enduring enigma. The present work provides exactly that: it propels BaCo₂(AsO₄)₂ to the forefront of research as a champion among Kitaev magnets, while bringing its multifaceted conundrums close to a complete resolution by reconciling its puzzling magnetic state, spectrum, and low critical field with the phenomenology of the proposed model.