Nanosculpted 3D helices of a magnetic Weyl semimetal with switchable nonreciprocity

The emergent properties of materials are defined by the symmetries of their underlying atomic, spin and charge order. The explorations of symmetry breaking effects are therefore usually limited by the intrinsic properties of known, stable materials. In recent years, advances in focused ion beam (FIB) fabrication have enabled the nanostructuring of bulk crystals into ultraprecise transport devices, facilitating the investigation of geometrical effects on mesoscopic length scales. In this talk, I will introduce FIB-sculpted three dimensional nanostructures, in the form of helical-shaped devices of the high-mobility Weyl magnet Co₃Sn₂S₂. The combination of the imposed chiral geometry and intrinsic ferromagnetism yields nonreciprocal electron transport. The high coercivity results in an anomalous, reversable diode effect remnant under zero applied magnetic field, which is orders of magnitude larger than can be explained by a classical self-field mechanism. We argue the enhancement originates from the high carrier mobility and the resulting quasi-ballistic transport: the conduction electron mean free path approaches the length scale of the geometrical curvature, resulting in increased asymmetrical scattering at the device boundaries. We further demonstrate that the nanostructure enables current-induced switching of the magnetisation. The results establish the vast potential of FIB-based sculpting to realise 3D nanostructures of single crystal quantum materials.