Spin density wave and van Hove singularity in the kagome metal CeTi₃Bi₄

The electronic band structure of kagome metals is the basis for a growing number of intriguing physical phenomena.  Here we focus on the case of Ce³⁺ pseudospin-1/2 (Jeff = 1/2) local moments coupled by a Ti-derived Kagome electronic structure in the material CeTi₃Bi₄.  Neutron scattering measurements under applied magnetic fields reveal that CeTi₃Bi₄ exhibits a rich temperature-field phase diagram where an incommensurate spin-density wave (SDW) ground state coexists with a commensurate magnetic modulation.  Remarkably, ARPES and DFT investigations reveal that the van Hove singularities (VHSs) of the kagome bands near the Fermi level are nested by vectors which coincide with the observed magnetic propagation vectors. This correspondence suggests a VHS-driven mechanism for SDW formation and provides an interesting counterpart to the charge density waves observed in other kagome metals. Our results establish that CeTi₃Bi₄ offers a rare opportunity to explore intertwined kagome Fermiology and quantum-magnetic spin textures.