Incommensurate magnetism drives singular angular magnetoresistance in the magnetic Weyl semimetal CeAlGe

Yao, X.*; Chen, P.*; Verma, R.*; Zhao, X.*; Yang, H.-Y.*; DeBeer-Schmitt, L.*; Aczel, A. A.*; Wu, C.-M.*; Alba-Venero, D.*; Ohara, Takashi   ; Munakata, Koji*; Takahashi, Miwako*; Noda, Yukio*; Bansil, A.*; Singh, B.*; Nikoli, P.*; Tafti, F.*; Gaudet, J.*

We demonstrate that a multi-k incommensurate magnetic state in the Weyl semimetal CeAlGe gives rise to a singular angular magnetoresistance (SAMR), which is an electrical transport signature capable of detecting magnetic field direction with exceptional precision. In contrast, its sister compound CeAlSi is devoid of both multi-k order and SAMR. We reveal that both phenomena appear upon 57% Ge substitution in CeAlSi1-xGex and coincide with electronic structure changes that soften the single-ion in-plane anisotropy and enhance Weyl-mediated magnetic interactions. These results unveil a remarkable connection between band topology, electronic transport, and collective magnetism in Weyl semimetals.