Nanoscale spin-polarized imaging of magnetic Weyl semimetal CeBi

Abstract

Weyl fermions are massless excitations with definite chirality. They manifest around band-touching points in the bulk band structure when inversion or time-reversal symmetry is broken. Among Weyl semimetals, those breaking time-reversal symmetry are of special interest due to their potential for the controlled manipulation of Weyl points through magnetic structure engineering. Here, we present a systematic investigation of the Weyl state in different magnetic phases of CeBi and report the discovery of a tunable magnetic Weyl semimetal state within nanoscale fully-polarized domains in the antiferromagnetic (++−−) CeBi. In the ferrimagnetic (+++−) phase, quasiparticle interference (QPI) measurements show a 100 meV band splitting in the Bi 6p band, which supports the existence of Weyl points in this phase. Similarly, in the fully-polarized (++++) state, we observed at least a 200 meV band splitting in the Bi 6p band along the kx axis, supporting the existence of Weyl nodes in fully-polarized CeBi. We demonstrate the creation of Weyl nodes by inducing local ferromagnetic (FM) domains in antiferromagnetic CeBi. These FM domains consist of co-aligned Ce moments and can be generated through in-plane magnetic field training or by employing a scanning tunneling microscopy (STM) tip to induce local strain. We image the formation of Weyl fermions around these FM domains by measuring QPI patterns. Our results not only demonstrate CeBi as an excellent magnetic Weyl semimetal for investigating intrinsic Weyl physics but also show the possibility of controllably writing the Weyl phase at the nanoscale. Finally, we present a novel way to accelerate QPI measurements by acquiring sparsely measured dI/dV maps and full-grid topography maps simultaneously. The acquired full-grid topography maps facilitate the computation of drifting phase maps, essential for correcting lattice distortions within reconstructed dI/dV maps. Our results demonstrate the effectiveness of sparse sampling, thereby broadening the scope of QPI applications.