X-ray Natural Circular Dichroism as a future probe for average chirality in amorphous B20 chiral topological semimetals

Chiral topological semimetals from the B20 family such as PtGa and PdGa are a novel class of material, shown to have unique spin- and orbital angular momentum-textures. As such, they have many potential uses in new orbitronic logic and memory devices. Additional recent theoretical work suggests that orbital angular momentum monopoles – sources and sinks of Berry curvature – may persist when the material is made amorphous, due to a fixed local chirality. Amorphous materials would be cheaper and more scalable, so would be ideal for use in novel devices. However, a measurement technique is needed to observe the average chirality in such an amorphous material. It has been theorized that these B20 materials display X-ray Natural Circular Dichroism (XNCD), a dichroic absorption of X-rays in the absence of magnetic ions due to their structural chirality. In crystalline B20 materials, the effect is proposed to be largest along the chiral winding axis (the [111] direction), and to vanish along the [001] direction. We plan to demonstrate this effect in crystalline PtGa and PdGa, show its angular dependence, and that it persists from base to room temperature. Demonstrating this XNCD effect in crystalline B20s opens the door to using XNCD as a probe for average chirality for amorphous B20s in the future.