Charting the Bend where Electrons Dwell in Kagome Substances

June 16, 2023 feature

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by Ingrid Fadelli , Phys.org

Kagome metals have a unique lattice structure resembling Japanese woven bamboo patterns with interesting properties that make them a class of quantum materials. Physicists have been studying these materials over the past ten years to explore various electronic phenomena that are a result of their unique structure.

University of Bologna, University of Venice, CNR-IOM of Trieste, University of Würzburg, and other European and American institutes collaborated on a recent study. They explored the spin and electronic structure of materials in the XV6Sn6 family, a type of Kagome metal, which is partially composed of a rare-earth element. They published their paper in Nature Physics, documenting the behavior of electrons residing in a curved space in these materials known as spin Berry curvature.

'Kagome metals belong to a class of new quantum materials that is revolutionizing the way material scientists look at complex collective phenomena, such as magnetism and superconductivity,' said Domenico Di Sante, one of the researchers involved in the study. 'We have been working on Kagome metals for several years, and this paper came out as a natural continuation of our previous works. The primary objective was to detect the curvature of the space where some of the electrons in Kagome metals live.'

Di Sante and his colleagues used both theoretical and experimental methods to explore the spin Berry curvature in the XV6Sn6 Kagome family. They first used advanced computing software to simulate the materials, before using angle-resolved photoemission spectroscopy to examine samples of ScV6Sn6 Kagome metal.

'From the theoretical viewpoint we used modern and very powerful supercomputers to model, via sophisticated software, the behavior of electrons inside the Kagome metals,' Di Sante said. 'From the experimental side, we needed to use the light that can be generated only at large-scale facilities such as synchrotrons to detect the energy and velocity of the electrons, simultaneously to their spin.'

The researchers' simulations and experiments led to several interesting observations. They gathered evidence of a finite spin Berry curvature at the center of the Brillouin zone, where the materials' nearly flat band detached from the so-called Dirac band, due to a physical phenomenon known as spin-orbit coupling. When they examined a sample of ScV6Sn6, the team found that in this material the spin Berry curvature was robust against the onset of an ordered phase driven by changes in temperature.

'The most notable contribution of our work is the application of a well-defined protocol, i.e., the use of light, circular dichroism and spin resolution, to map out the curved space where the electrons live,' Di Sante said. 'In a similar way the space-time of our universe is curved by matter, stars, galaxies, black holes etc, the space where the electrons move can be curved. Our work detected one of these curvatures in Kagome metals.'

Through their recent work, the team collected additional valuable insight about the electronic structure and spectroscopic fingerprint of Kagome metals in the XV6Sn6 family. Their observations could pave the way for new studies into the unique qualities of these materials and their possible technological applications in the future.

'In our next works, we plan to continue investigating this class of materials,' added Di Sante. 'There are other families of Kagome metals that promise to enrich our understanding of collective phenomena and their link to the field of topology (curved spaces are intimately linked to the concept of topology).'

Journal information: Nature Physics

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