With the help of “kagome materials,” a brand-new class of quantum materials, a multidisciplinary research team has successfully measured the electron spin in matter for the first time, that is, the curvature of space in which electrons reside and flow.
Three perspectives of the surface on which the electrons move. On the left, the experimental result, in the center and on the right the theoretical modeling. The red and blue colors represent a measure of the speed of the electrons. Both theory and experiment reflect the symmetry of the crystal, very similar to the texture of traditional Japanese “kagome” baskets. Image Credit: Wits University
The findings, which were reported in the journal Nature Physics, have the potential to fundamentally alter how quantum materials are studied in the future.
This will pave the way for new quantum technology developments that could find use in a wide range of industries, from electronics to biomedicine to renewable energy and quantum computing.
Domenico Di Sante, professor in the Department of Physics and Astronomy “Augusto Righi”, participated for the University of Bologna as part of his Marie Curie BITMAP research project in an international partnership of scientists that resulted in success.
Colleagues from Boston College, University of Santa Barbara (USA), Ca’ Foscari University of Venice, University of Milan, CNR-IOM Trieste, University of Würzburg (Germany), and University of St. Andrews (UK) joined him.
The researchers were able to detect electron spin for the first time, which is connected to the idea of topology, utilizing cutting-edge experimental techniques employing light produced by a particle accelerator, the Synchrotron, and with the help of contemporary methodologies for modeling the behavior of matter.
If we take two objects such as a football and a doughnut, we notice that their specific shapes determine different topological properties, for example because the doughnut has a hole, while the football does not. Similarly, the behavior of electrons in materials is influenced by certain quantum properties that determine their spinning in the matter in which they are found, similar to how the trajectory of light in the universe is modified by the presence of stars, black holes, dark matter, and dark energy, which bend time and space.
Domenico Di Sante, Professor, Department of Physics and Astronomy, University of Bologna
Despite the fact that this property of electrons has been known for a long time, no one has ever been able to directly detect this “topological spin” before.
The researchers did this by making use of a phenomenon known as “circular dichroism”—a unique experimental method that can only be employed with a synchrotron source—which takes advantage of the ability of materials to absorb light differently depending on their polarization.
Researchers have concentrated particularly on “kagome materials,” a type of quantum materials so named because of their resemblance to the bamboo baskets that are traditionally made in Japan and are also known as “kagome.”
These materials are transforming quantum physics, and the findings could shed light on their unique magnetic, topological, and superconducting characteristics.
Di Sante added, “These important results were possible thanks to a strong synergy between experimental practice and theoretical analysis. The team’s theoretical researchers employed sophisticated quantum simulations, only possible with the use of powerful supercomputers, and in this way guided their experimental colleagues to the specific area of the material where the circular dichroism effect could be measured.”
The study was titled “Flat band separation and robust spin Berry curvature in bilayer kagome metals” and was published in Nature Physics. Domenico Di Sante, a researcher from the University of Bologna’s “Augusto Righi” Department of Physics and Astronomy, is the study’s first author.
He collaborated with researchers from the CNR-IOM in Trieste, the Ca’ Foscari University in Venice, the University of Milan, the University of Würzburg in Germany, the University of St. Andrews in the United Kingdom, Boston College, and the University of Santa Barbara in the United States.
Journal Reference
Di Sante, D., et al. (2023) Flat band separation and robust spin Berry curvature in bilayer kagome metals. Nature Physics. doi:10.1038/s41567-023-02053-z