Chiral and magnetic topological semimetals

Chiral topological semimetals (which possess neither mirror nor inversion symmetries) are expected host numerous novel phenomena, such as multifold fermions with large topological charge, long Fermi-arc surface states, unusual magnetotransport and lattice dynamics, and a quantized response to circularly polarized light. Until recently, all experimentally confirmed topological semimetals crystallized in space groups that contain mirror operations, which means that the aforementioned phenomena vanish [1].

Here, I will present evidence from angle-resolved photoelectron spectroscopy that a family of intermetallic catalysts, including PtAl and PdGa [1,2], are chiral topological semimetals. We directly visualize the exotic multifold fermions in these materials and show that they carry the largest possible Chern number that is available in any material. We also show experimentally that there is a direct relationship between the handedness of the crystal structure and the electronic chirality (i.e. the Chern number sign) of the multifold fermions. This finding demonstrates that structural chirality can be used as a tuning knob to control e.g. the direction of topological photocurrents, which is sensitive to the Chern number sign.

Furthermore, I present evidence for multifold fermions in structurally chiral magnetic materials and show that CoS₂ - a putative half-metal - is in fact not-half metallic, but may host topological surface states that could affect its performance as a spin-injector.

[1] N. B. M. Schröter et al., Nat. Phys. 15, 759–765 (2019).
[2] N. B. M. Schröter et al., arXiv 1907.08723 (2019).