Exciting and Probing Topological Quantum States in PrAlGe Weyl Magnets

Weyl semimetals host massless, chiral electrons, which attract interest due to their unique topological properties and exotic quantum phenomena, including the chiral anomaly and Fermi arc surface states. Magnetic Weyl semimetals introduce an additional layer of complexity due to their dependence on magnetism, thereby creating new opportunities for controlling their topological properties. We have studied a mid-infrared chiral photoresponse in the PrAlGe magnetic Weyl semimetal, observing the excitation and probing of chiral electrons from two different linear dispersion energy bands—Weyl bands—near the Fermi level. The signature of photoexcited chiral electrons is observed alongside the ferromagnetic phase transition below the Curie temperature. A step-like chiral photoresponse coincides with the onset of ferromagnetic order. This response is highly sensitive to the helicity of incident mid-infrared light, suggesting that circularly polarized light can selectively excite Weyl bands activated by magnetic symmetry breaking. Due to the proximity of multiple Weyl bands near the Fermi level, low-energy far-infrared polarimetry is needed to reveal the signature of each Weyl band.