Magnetic Domains in the Strongly Correlated Weyl Semimetal Candidate CeBi*

Weyl Fermions can arise from Dirac semimetals when the degenerate massless states are split by broken time-reversal symmetry into two bands with opposite chirality. Recently, such states have been predicted in the strongly correlated cerium monopnictides, which develop band inversion as spin orbit coupling increases, and are known to host complex magnetic phase diagrams. Thus cerium monopnictides are ideal materials for studying the interplay of magnetism and topology. Here, we use spin-polarized scanning tunneling microscopy to map the magnetic phases of CeSb and CeBi on the atomic scale. We find distinct magnetic domains with differing spin periodicities, separated by abrupt domain walls. Furthermore, we observe quasiparticle scattering from the domain walls and defects in both materials. Control of these magnetic phases in cerium monopnictides provides the possibility of tuning the key energy scales and momentum splitting of Weyl fermions.