Unexpected band structure changes within the higher-temperature antiferromagnetic state of CeBi

The interest in the rare-earth monopnictides was boosted after the discovery of unconventional surface-state pairs in antiferromagnetically ordered NdBi. In contrast to other materials in which such states were reported, CeBi is known to have multiple antiferromagnetic phases. In this study, we perform angle-resolved photoemission spectroscopy (ARPES) measurements in conjunction with density functional theory (DFT) calculations to investigate the evolution of the electronic structure of CeBi upon a series of antiferromagnetic (AFM) transitions. We find evidence for a new AFM transition in addition to two previously known from transport studies. We demonstrate the development of an additional Dirac state in the ( + − + − ) ordered phase and a transformation of unconventional surface-state pairs in the ( + + − − ) ordered phase. This revises the phase diagram of this intriguing material, where there are now three distinct AFM states below TN in zero magnetic field instead of two as it was previously thought. Rare-earth mono-pnictides antiferromagnets have generated recent interest as hosts to topological states and unconventional magnetic states. Here, angle-resolved photoemission spectroscopy reveals a hidden band-structure transition within the higher-temperature antiferromagnetic state of CeBi.