Structure-driven topological phase transition in a quasi-one-dimensional ferromagnetic Weyl semi-metal

The quasi-one-dimensional compound K₂Cr₈O₁₆ is famous for exhibiting a structure-driven ferromagnetic-metal-to-ferromagnetic-insulator transition (FM-MIT), a transition not explained by the Hubbard model. Since the doped metallic phase of K₂Cr₈O₁₆ belongs to the special class of magnetic Weyl semimetals, this FM-MIT is also a topological phase transition. In this work, we show that the unique topological phase transition from a trivial insulator to a topological magnetic Weyl semimetals is structure driven, and can be achieved using temperature as the tuning parameter. Through inelastic X-ray and neutron scattering experiments combined with first-principles theoretical calculations, we demonstrate the absence of divergences in the electronic and magnetic responses across the transition, disproving the previous proposition that this transition is driven by a Peierls instability. We further establish that the exchange interaction is mainly superexchange in nature, which persists across the transition, as opposed to double-exchange type as previously proposed. This work represents the first systematic study of a topological phase transition for a structure driven ferromagnetic Weyl semimetal, paving way for novel topological spintronics devices.