Scientists use quantum materials to create "3D glasses"-like viewing angles to visualize topological materials

Topological quantum materials are seen as a beacon of hope for energy-efficient electronics and future high technologies. A distinctive feature of these materials is their ability to conduct spin-polarized electrons on their surfaces while being non-conductive inside. Look at it this way: In a spin-polarized electron, the intrinsic angular momentum, i.e. the direction of rotation of the particle (spin), is not purely randomly arranged.

The researchers used X-rays (green part in the picture) to create a three-dimensional movie-like effect on the metal TbV6Sn6. Using this method, they successfully tracked the behavior of electrons (blue and yellow in the image) and took a step forward in understanding quantum materials. Image source: Jörg Bandmann/ct.qmat)

To distinguish topological materials from traditional materials, scientists are accustomed to studying their surface currents. However, the topology of an electron is closely related to its quantum mechanical wave properties and spin. Now, this relationship has been directly demonstrated through the photoelectric effect - the release of electrons from materials such as metals under the influence of light.

Professor Giorgio Sangiovanni, a founding member of ct.qmat in Würzburg and one of the theoretical physicists on the project, compared the discovery to using 3D glasses to observe the topology of electrons. He explained that "electrons and photons can be described quantum mechanically as waves and particles. Therefore, electrons have spin, and we can measure the spin of electrons using the photoelectric effect."

To do this, the research team used circularly polarized X-ray light - light particles with a torque. Sangiovanni explained in detail: "When a photon encounters an electron, the signal emitted by the quantum material depends on whether the photon spins right or left. In other words, the direction of the electron's spin determines the signal between the left-handed and right-handed beams. The relative intensity. Therefore, we can think of this experiment as polarized glasses in a 3D cinema, where beams of light in different directions are also used to make the topology of the electrons clearly visible."

This groundbreaking experiment and its theoretical description, led by the Würzburg-Dresden Excellence Research Group ct.qmat (Complexity and Topology in Quantum Matter), are the first successes in characterizing quantum materials from a topological perspective. try. Sangiovanni pointed out the important role of particle accelerators in the experiment, saying: "We need synchrotrons to produce this special X-ray light and create the '3D movie' effect."

It took the researchers three years to finally achieve this great success. Their starting point was the quantum material "Kagome" metal TbV6Sn6. In this particular class of materials, the atomic lattice is a mixture of triangular and honeycomb lattices, with a structure reminiscent of Japanese basket weaving. Shikame Metal plays an important role in ct.qmat’s materials research.

"Before our experimental colleagues started the synchrotron experiments, we needed to simulate the experimental results to make sure we were on the right track. As a first step, we designed the theoretical model and performed the calculations on a supercomputer," said the project leader said Dr. Domenico di Sante, theoretical physicist and associate member of the Würzburg Collaborative Research Center (SFB) 1170 ToCoTronics. The measurements matched theoretical predictions perfectly, allowing the team to visually visualize and confirm Kagome's metallic topology.

The scientists involved in the research project come from Italy (Bologna, Milan, Trieste, Venice), the United Kingdom (St. Andrews), the United States (Boston, Santa Barbara) and Würzburg. The supercomputer used for the simulations is in Munich and the synchrotron experiments are conducted in Trieste. "Professor Sangiovanni concluded: "These research results perfectly illustrate the extraordinary results that theoretical physics and experimental physics can produce when they work together.