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Schematic diagram of magnetic resonance and field-induced splitting of excitation. The gray line indicates the zero magnetic field d.I/dU (above) and d2I/dU2 (Bottom) Spectrum and red (blue) dashed lines represent the majority (minority) contribution of the magnetic field splitting resonance/excitation. Arrows indicate the direction of shift with increasing field strength. beFano curve derived from Kondo resonance. b, a bias symmetry step reflecting inelastic tunneling of electrons that causes excitation of the spins of the system. Similar to the Kondo system feature, most (few) spin excitations shift to lower (higher) energies. cconversely, spinaron appears prominently as the peak of d2I/dU2 The signal in the majority channel is shifted to higher energies even though it has most of the spin characteristics, while all other features representing spin excitations are shifted as shown in the figure. b. Credit: https://www.nature.com/articles/s41567-023-02262-6
Experimental physicists at the Würzburg-Dresden Cluster of Excellence ct.qmat have demonstrated for the first time a new quantum effect, aptly named the ‘spinalon’. Using a carefully controlled environment and a sophisticated set of equipment, they were able to demonstrate the unusual state that cobalt atoms assume on the surface of copper.
This revelation calls into question the long-held Kondo effect, a theoretical concept developed in the 1960s and considered the standard model for the interaction of magnetic materials and metals since the 1980s. These groundbreaking discoveries published Today is natural physics.
Ultra-cold and ultra-strong: pushing the limits of the lab
Extreme conditions prevail in the Wurzburg laboratory of experimental physicists Professor Matthias Bode and Dr. Artem Odobösko. These visionaries from the Cluster of Excellence ct.qmat, a collaboration between JMU Würzburg and the Technical University of Dresden, are setting new milestones in quantum research.
Their latest effort is to uncover the spinaron effect. They placed individual cobalt atoms strategically on the surface of the copper, lowered the temperature to what he called 1.4 Kelvin (–271.75 degrees Celsius), and exposed it to a strong external magnetic field. “The magnets we use cost 500,000 euros. They are not widely available,” Bode says. Subsequent analysis revealed an unexpected fact.
“Using a scanning tunneling microscope, we can see individual cobalt atoms. Each atom has a spin, which you can think of as a magnetic north or south pole. Measuring it It was critical to an amazing discovery,” Bode explains. “We deposited magnetic cobalt atoms onto a non-magnetic copper base and allowed the atoms to interact with the copper’s electrons.” The study of such correlated effects within quantum materials is central to ct.qmat’s mission. It is a pursuit that promises radical technological innovation in the future.
Since the 1960s, solid-state physicists have believed that the interaction between cobalt and copper can be explained by the Kondo effect, because the different magnetic orientations of cobalt atoms and copper electrons cancel each other out. This creates a state in which the copper electrons bond to the cobalt atoms, forming what is known as a “Kondo cloud.”
But Bode and his team dug deeper into the lab. And they tested an alternative theory proposed in 2020 by Samir Rounis, a theorist at the Jülich Institute.
Physicists in Würzburg have succeeded in determining the magnetic direction of spins in cobalt by harnessing the power of a strong external magnetic field and using an iron tip in a scanning tunneling microscope. This spin is not fixed, but permanently switches back and forth. That is, from “spin up” (positive) to “spin down” (negative) and vice versa. This switching excites the electrons in the copper, a phenomenon called the spinaron effect.
Bode explains this with a vivid analogy. “The state of a cobalt atom can be compared to a rugby ball because the spin arrangement is constantly changing. When a rugby ball rotates continuously in a ball pit, the surrounding balls are displaced. That’s exactly what we do. observed – the electrons in the copper began to vibrate in response and bonded with the cobalt atoms.
“The combination of the changing magnetization of the cobalt atom and the electrons of the copper to which it is bound is the spinaron predicted by our colleague Urich.”
The first experimental verification of the spinaron effect, courtesy of the Wurzburg team, casts doubt on the Kondo effect. Until now, it was considered a universal model to explain the interaction between magnetic atoms and electrons in quantum materials such as the cobalt-copper duo. “It’s time to pencil in that important asterisk in your physics textbook,” Bode quipped.
spinaron and spintronics
In the spinaron effect, cobalt atoms remain in perpetual motion and maintain their magnetic nature despite interactions with electrons. On the other hand, in the Kondo effect, the magnetic moment is neutralized by electronic interactions.
“Our findings are important for understanding the physics of magnetic moments on metal surfaces,” Bode says. Looking to the future, such phenomena could pave the way for the encoding and transfer of magnetic information in new types of electronic devices. This technology, called “spintronics,” has the potential to make IT greener and more energy efficient.
But Bode tempers expectations when he talks about the practicality of this cobalt and copper combination. “We essentially manipulated individual atoms at ultracold temperatures on pure surfaces in ultra-high vacuum. That’s not possible with a cell phone. Correlation effects are a branch in fundamental research for understanding the behavior of materials. point, but I can’t do that.” Don’t build an actual switch from there. ”
Currently, Würzburg quantum physicist Artem Odvesko and Jülich theorist Samir Rounis are concentrating on an extensive review of the numerous publications that have described the Kondo effect in various combinations of materials since the 1960s. “Many people doubt that we actually have an explanation for the spinaron effect,” Odvesko said. “If so, it would rewrite the history of theoretical quantum physics.” added.
For more information:
Felix Friedrich et al, Evidence for spinaron in Co adatoms, natural physics (2023). DOI: 10.1038/s41567-023-02262-6. www.nature.com/articles/s41567-023-02262-6
Provided by Wurzburg Dresdner Exzellenzcluster