Spin-polarized imaging of strongly interacting fermions in the magnetic phases of Weyl candidate CeBi

CeBi has a rich magnetic phase diagram and several predicted topological states that vary with magnetic phase. Here we focus on the ferrimagnetic and fully-polarized phases of CeBi, where our density functional theory (DFT) calculations predict several Weyl nodes near the Fermi level (E_f). We use spin-polarized scanning tunneling microscopy (SP-STM) and spectroscopy to image the surface magnetic order, and quasiparticle interference (QPI) imaging to quantify the band splitting of the ferrimagnetic and fully polarized phases with respect to the ground antiferromagnetic phase. In the ferrimagnetic phase, strong suppression of the surface spin-polarization at E_f, coincident with a Fano line shape in dI/dV, suggests the Bi p states partially Kondo screen the f magnetic moments, and this p-f mixing causes strong Fermi-level band renormalization. The QPI measurements support p band flattening and ~100 meV splitting, suggesting a strongly interacting magnetic Weyl semimetal with robustly spaced Weyl nodes. In fully polarized CeBi, on the (001) surface we discover that the outer Bi 6p band splits by ~ 200 meV, which is large enough to overcome the hybridization gap and give rise to a magnetic Weyl state. Our SP-STM and QPI measurements in three magnetic phases of CeBi paint a consistent picture of a strongly interacting magnetic Weyl semimetal that can be driven between different topological phases with the external field.