Quantum materials: electron spin measured for the first time

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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. Credits: University of Bologna

An international research group has succeeded for the first time in measuring the spin of the electron in matter, i.e. the curvature of the space in which electrons live and move within “kagome materials”, a new class of quantum materials.

The obtained results published in Physics of natureit could revolutionize the way quantum materials are studied in the future, opening the door to new developments in quantum technologies, with possible applications in a variety of technological fields, from renewable energy to biomedicine, from electronics to quantum computers.

The success was achieved by an international collaboration of scientists, in which Domenico Di Sante, professor at the “Augusto Righi” Department of Physics and Astronomy, participated for the University of Bologna as part of his Marie Curie research project BITMAP . He was joined by colleagues from the CNR-IOM of Trieste, the Ca’ Foscari University of Venice, the University of Milan, the University of Wrzburg (Germany), the University of St. Andrews (UK) , Boston College and the University of Santa Barbara (USA).

Through advanced experimental techniques, using the light generated by a particle accelerator, the synchrotron, and thanks to modern techniques for modeling the behavior of matter, scholars have been able to measure for the first time the spin of the electron, linked to the topology concept.

“If we take two objects like a soccer ball and a donut, we notice that their specific shapes determine different topological properties, for example because the donut has a hole, while the ball doesn’t,” explains Domenico Di Sante. “Similarly, the behavior of electrons in materials is influenced by some quantum properties that determine their rotation in the matter in which they are located, similarly to how the trajectory of light in the universe is modified by the presence of stars, black holes, matter and dark energy, which bend time and space.”

Although this characteristic of electrons has been known for many years, no one has been able to measure this “topological spin” directly until now. To achieve this, the researchers exploited a particular effect known as “circular dichroism”: a particular experimental technique that can only be used with a synchrotron source, which exploits the ability of materials to absorb light in different ways depending on their polarization.

Scholars have focused in particular on “kagome materials”, a class of quantum materials that owe their name to their resemblance to the weaving of woven bamboo threads that make up a traditional Japanese basket (called “kagome”). . These materials are revolutionizing quantum physics and the results obtained could help us better understand their special magnetic, topological and superconducting properties.

“These important results were possible thanks to a strong synergy between experimental practice and theoretical analysis”, adds Di Sante. ‘The theoretical researchers in the team employed sophisticated quantum simulations, which are only possible with the use of powerful supercomputers, and in doing so guided their experimental colleagues to the specific area of ​​the material where the effect of circular dichroism could be measured. “.

More information:
Domenico Di Sante et al, Flat Band Separation and Strong Spin Berry Curvature in Bilayer Kagome Metals, Physics of nature (2023). DOI: 10.1038/s41567-023-02053-z

About the magazine:
Physics of nature

Provided by the University of Bologna

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