Researchers built a simple theoretical model to show how strong electron interactions in a chiral crystal can create chiral Weyl quasiparticles right at the Fermi energy. These quasiparticles are heavy because they come from the Kondo effect, a process in which localized magnetic moments become entangled with conduction electrons and form narrow, low-energy bands. The team then calculated a nonlinear optical response, the circular photogalvanic effect (CPGE), and found sharp frequency peaks that they identify as clear signatures of these Kondo-driven chiral Weyl nodes.

To make the problem tractable, the authors constructed a prototype Kondo lattice model that keeps only the key couplings required by the crystal symmetry of space group no. 78, a chiral, tetragonal structure relevant to the candidate material CeGaGe. The model places one itinerant (conduction) electron and one localized electron on each of four symmetry-related sites in the unit cell. The conduction electrons have simple hoppings and spin-orbit coupling. The conduction and localized electrons are coupled through the periodic Anderson model, and the authors focus on the strongly correlated limit in which on-site Coulomb repulsion is very large. They treat the local constraint that forbids double occupation using a standard parton method and a saddle-point approximation, which produces renormalized hybridization and narrow, heavy-electron bands set by a Kondo energy scale.

The work emphasizes how crystal symmetries force specific topological features in the heavy-quasiparticle spectrum. With time-reversal symmetry and spin-orbit coupling, screw and other nonsymmorphic symmetries lead to distinctive band connectivities often called “accordion” and “hourglass” types. These enforced connectivities produce symmetry-enforced Weyl points and even a Weyl nodal plane in the quasiparticle bands. Because the crystal itself is chiral, the model also has Kramers–Weyl points at the time-reversal-invariant momenta. The authors numerically evaluate the topological chiral charges of several of these Weyl nodes in the heavy bands.