William Gannon - University of Kentucky

Title: Neutron Diffraction and Magnetotransport Studies of the Candidate Weyl Semimetal CeGaGe

Abstract: The RXZ (R = rare-earth, X = Al or Ga, Z = Si or Ge) family of materials is thought to crystallize with symmetry described by the noncentrosymmetric I41md space group. Band structure calculations of many members of this family predict Weyl semimetal behavior with topologically protected surface states. 

When the rare-earth ions carry a magnetic moment, these materials also exhibit magnetic order, allowing Weyl states above the ordering temperature and enabling studies of the interplay between Weyl quasiparticles and magnetic excitations below it. 

The magnetic order in these compounds is often nontrivial and tied precisely to material composition [1, for example]. The compound CeGaGe belongs to this family. Depending on crystal growth conditions, we find that samples can undergo a subtle structural transition to another noncentrosymmetric structure, with symmetry described by space group P43, at temperatures above about 100 K [2]. 

Regardless of low-temperature structure, all samples show a clear transition to a magnetically ordered state at Tc = 5.5 K [2,3]. I will present our ongoing neutron diffraction studies characterizing the crystal and magnetic structures of CeGaGe with varying stoichiometry, revealing a complex relation between composition, ferromagnetic order, and chiral ordered states. I will also discuss our magnetotransport measurements and their relation to these ordered magnetic states.

[1] X. Yao et al., Phys. Rev. Lett. 136, 086702 (2026).
[2] L. Scanlon et al., Phys. Rev. B 111, 184102 (2025).
[3] D. Ram,  et al, Phys. Rev. B 108, 024428 (2023).