Miwako Takahashi

The microscopic origin of the low-field 1/9 magnetization plateau in spin-1/2 kagome antiferromagnets remains unresolved. Here we show that chemical pressure reshapes the hierarchy of fractional plateaus in the titanium-based kagome family Cs8AB3Ti12F48 (A = Rb, Li; B = K, Na). High-field measurements up to 60 T reveal a robust 1/9 plateau-like phase in the expanded Cs8RbK3Ti12F48 and Cs8LiK3Ti12F48 compounds, despite the absence of the conventionally more robust 1/3 plateau. In contrast, compressed Cs8LiNa3Ti12F48 exhibits neither the 1/9 plateau-like phase nor a quantum-disordered ground state. Specific heat measurements and first-principles calculations show that lattice expansion preserves a frustrated, fully connected kagome exchange network and gapless quantum-disordered ground states, whereas compression reorganizes the network into weakly coupled quasi-one-dimensional subsystems and induces successive magnetic transitions. These results demonstrate that the 1/9 and 1/3 plateaus need not share a common microscopic origin and suggest that the 1/9 plateau may be a more universal feature of frustrated spin-1/2 kagome magnetism.

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 CeAlSi_{1-x}Ge_{x} 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.