Experimental and theoretical re-evaluation of a putative Weyl 'Hydrogen-atom*

Often in the search for new exotic phases of matter we turn to a priori predictions of material's properties to guide our way. This is commonly met with mixed results due to the complexity of real materials as compared with their idealized theoretical counterparts. In this talk I will present the results of the study of a material so identified as a potential Weyl 'Hydrogen atom,' that is a semi-metal with only a single pair of Weyl nodes at the Fermi energy. Such a material is highly sought to study and harness the exotic physics associated with these topological nodes such as the chiral anomaly, unclosed surface Fermi arcs, and even potentially topological superconductivity. I will discuss the synthesis, structure and magnetic properties of this candidate material and consider how they theoretically are expected to influence the topological properties. Of key interest is the finding of multiple magnetic transitions one of which realizes a magnetic structure that exhibits the symmetry predicted to generate a pair of Weyl nodes. Yet other measurements reveal only insulating behavior inconsistent with the predicted semi-metallic band structure. This leads to questions of why there is such a disparity between the calculated properties and those observed and whether there is a way to push the real material closer to the theoretical model