Quantum physicists at the Würzburg-Dresden Cluster of Excellence ct.qmat have made a groundbreaking discovery that challenges long-held beliefs about magnetic interactions in quantum materials. Their research has revealed the existence of a remarkable effect called the spinaron, shedding new light on the mysteries of quantum physics.

Under the guidance of experimental physicists Professor Matthias Bode and Dr. Artem Odobesko, the scientists conducted their experiments in the extraordinary laboratory conditions of the Würzburg facility. By placing individual cobalt atoms onto a copper surface and subjecting them to an intense magnetic field at extremely low temperatures, they were able to observe unexpected phenomena.

The team employed a scanning tunneling microscope to examine the cobalt atoms. Each atom possesses a magnetic property known as spin, akin to a north or south pole. Measuring the spin was crucial in their quest for new discoveries. Through the interaction of the magnetic cobalt atoms with the electrons of the non-magnetic copper base, they uncovered correlation effects within quantum materials, which is the primary focus of the ct.qmat initiative. This line of research holds immense promise for future technological advancements.

In contrast to the conventional understanding of the interaction between cobalt and copper based on the Kondo effect, the Würzburg scientists validated an alternative theory proposed by theorist Samir Lounis. By utilizing an iron tip in the scanning tunneling microscope and leveraging a powerful external magnetic field, they observed that the cobalt’s spin constantly switches back and forth between positive and negative states. This dynamic behavior leads to the exciting of the copper electrons, a phenomenon they have dubbed the spinaron effect.

To better grasp this concept, Bode likens the state of the cobalt atom to a spinning rugby ball in a ball pit. The continuous motion of the rugby ball displaces the surrounding balls in a wave-like pattern. Similarly, the oscillation of the copper electrons is a response to the changing magnetization of the cobalt atom, resulting in a bonding between the two. This unique combination is precisely what the Jülich colleague predicted as the spinaron.

This groundbreaking experimental validation of the spinaron effect challenges the previously accepted Kondo effect, which has long been regarded as the universal model for explaining the interaction between magnetic atoms and electrons in quantum materials like cobalt and copper. The implications of this discovery are far-reaching, as it opens up new possibilities for magnetic information encoding and transport in advanced electronic devices, also known as spintronics.

However, Bode emphasizes that practical applications of this cobalt-copper combination are currently limited. The experiments conducted in the laboratory involve manipulating individual atoms at ultra-low temperatures and in ultra-high vacuum conditions, which are not feasible for everyday consumer devices. Nevertheless, the fundamental insights gained from this research are critical for understanding the behavior of matter and may pave the way for future technological advancements.

The researchers are now embarking on a comprehensive review of numerous publications that have described the Kondo effect in different combinations of materials since the 1960s. They suspect that many of these earlier studies might actually be describing the spinaron effect, suggesting a potential revision of the history of theoretical quantum physics.

The Cluster of Excellence ct.qmat, jointly operated by Julius-Maximilians-Universität Würzburg and Technische Universität Dresden, serves as the nexus for this cutting-edge research. With nearly 400 scientists from various countries and continents, the ct.qmat initiative focuses on studying topological quantum materials and their peculiar behaviors under extreme conditions. The project is funded through the German Excellence Strategy of the Federal and State Governments and represents the only Cluster of Excellence in Germany based in two different federal states.

Reference: “Evidence for spinarons in Co adatoms” by Felix Friedrich, Artem Odobesko, Juba Bouaziz, Samir Lounis and Matthias Bode, 26 October 2023, [Nature Physics](https://www.nature.com/nphys)