They are seen as a beacon of hope for energy-saving electronics and the high-tech of the future: topological quantum materials. One of their properties is to conduct spin-polarized electrons on their surface—even though they are actually non-conductive inside. To put it into perspective: In spin-polarized electrons, the intrinsic angular momentum, ie the direction of rotation of the particles (spin), is not purely randomly aligned.
To distinguish topological materials from ordinary ones, scientists used to study their surface currents. However, the topology of an electron is closely related to its quantum mechanical wave properties and its spin. This relationship is now directly demonstrated by the photoelectric effect—a phenomenon in which electrons are released from a material, such as a metal, with the help of light.
Giorgio Sangiovanni, a founding member of ct.qmat in Würzburg and one of the project’s theoretical physicists, likened this discovery to using 3D glasses to visualize the topology of electrons. He explained, “Electrons and photons can be described quantum mechanically like waves and particles. Therefore, electrons have a spin that we can measure thanks to the photoelectric effect.”
To do this, the team used circularly polarized X-ray light—light particles with torque. Sangiovanni explains, “When a photon meets an electron, the signal coming from the quantum material depends on whether the photon has right- or left-handed polarization.”
“In other words, the orientation of the spin of the electron determines the relative strength of the signal between the left and right polarized beams. Therefore, this experiment can be thought of as polarized glasses in a 3D cinema , where differently oriented light beams are also used. Our ‘3D glasses’ make the electrons’ topology visible.”
Led by the Würzburg-Dresden Cluster of Excellence ct.qmat—Complexity and Topology in Quantum Matter—this ground-breaking experiment, along with its theoretical description, is the first successful attempt to characterize quantum materials topologically. Sangiovanni pointed out the important role of a particle accelerator in the experiment, saying, “We need the synchrotron particle accelerator to generate this special X-ray light and to create the ‘3D cinema’ effect.”
Quantum matter, particle accelerators and supercomputers
The journey to this great achievement took three years for the researchers. Their beginning is kagome metal TbV6Sn6, a quantum material. In this special class of materials, the atomic lattice has a mixture of triangular and honeycomb lattices in a structure reminiscent of Japanese basket weave. Kagome metals play an important role in ct.qmat materials research.
“Before our colleagues started experimenting with the synchrotron experiment, we had to simulate the results to make sure we were on the right track. In the first step, we created theoretical models and ran the calculations on a supercomputer,” said Dr. Domenico di Sante , the project leader and a theoretical physicist, who is also an associate member of the Würzburg Collaborative Research Center (SFB) 1170 ToCoTronics.
The findings from the measurements perfectly lined up with theoretical predictions, enabling the team to visualize and confirm the topology of kagome metals.
The paper was published in Zenodo preprint server.
Domenico Di Sante et al, Flat band separation and strong spin-Berry curvature in bilayer kagome metals, Zenodo (2023) DOI: 10.5281/zenodo.7787937
Provided by the University of Würzburg
Citation: Visualizing the topology of electrons with ‘3D glasses’ (2023, July 13) retrieved 13 July 2023 from https://phys.org/news/2023-07-visualizing-topology-electrons-3d- glasses.html
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