One way they do this is by ordering their magnetic states – spins that point either up or down – in the opposite direction to their neighbors’ spins. “The cool thing about this structure is that the geometry imposes interesting quantum constraints on the way the electrons are allowed to zoom around, somewhat analogous to how traffic roundabouts affect the flow of traffic and sometimes bring it to a stop.”īy nature, electrons avoid one another. “Kagome materials have taken the quantum materials world by storm recently,” Yi said. The iron-germanium materials are kagome lattice crystals, a much-studied family of materials featuring 2D arrangements of atoms reminiscent of the weave pattern in traditional Japanese kagome baskets, comprising equilateral triangles that touch at the corners. The study involved more than a dozen researchers from Rice University, Oak Ridge National Laboratory (ORNL), SLAC National Accelerator Laboratory, Lawrence Berkeley National Laboratory (LBNL), the University of Washington and the University of California, Berkeley, as well as the Weizmann Institute of Science in Israel and the Southern University of Science and Technology in China. “We found magnetism subtly modifies the landscape of electron energy states in the material in a way that both promotes and prepares for the formation of the charge density wave,” said Yi, a co-corresponding author of the paper. Now, in a paper in Nature Physics, Rice University physicists Ming Yi and Pengcheng Dai, together with many of their collaborators from the 2022 study, present an array of experimental evidence showing that their charge density wave discovery was rarer still, a case where the magnetic and electronic orders don’t simply coexist but are directly linked. Magnetism also arises from the collective self-organization of electron spins into ordered patterns, but those patterns rarely coexist with the patterns that produce the standing wave of electrons known as a charge density wave. Physicists were surprised in 2022 by the discovery that electrons in magnetic iron-germanium crystals could spontaneously and collectively organize their charges into a pattern featuring a charge density wave (see Novel kagome material saddled with magnetism and waves). (Left) Kagome lattice (middle) Fermi surface of the magnetic phase of iron-germanium before the onset of a charge density wave (right) Fermi surface of iron-germanium after the onset of a charge density wave.
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