In a study published in Nature Physics, Rice University physicists and collaborators presented an array of experimental evidence showing their charge density wave discovery was rarer than first thought–a case where the magnetic and electronic orders don’t simply coexist but are directly linked. Magnetism subtly modifies the landscape of electron energy states in the material that promotes and prepares for the formation of the charge density wave.
Iron-germanium materials are kagome lattice crystals featuring 2D arrangements of atoms similar to the weave pattern in traditional Japanese kagome baskets, having equilateral triangles that touch at the corners. With this structure, the geometry imposes quantum constraints on how the electrons can zoom around. Typically, electrons avoid one another.
When put onto kagome lattices, electrons can appear in a state where they are stuck and cannot go anywhere due to quantum interference effects. When they can’t move, the triangular arrangement produces a situation where each has three neighbors, and there is no way for electrons to collectively order all neighboring spins in opposite directions. The lattice restricts electrons in ways that “can have a direct impact on the observable properties of the material.”
The team used a combination of inelastic neutron scattering experiments and angle-resolved photoemission spectroscopy experiments. The probes allowed them to look at what the electrons and the lattice were doing as the charge density wave took shape. The team hypothesizes that charge order and magnetic order are linked in iron-germanium where magnetism forms first, preparing the way for charges to line up. The discovery indicates that there is a chance to learn about the self-organizational abilities of the fundamental particles of quantum materials.