by Ingrid Fadelli
Credit: Pacu Moca.
Physicists worldwide have been investigating the behavior of hybrid nanostructures. These systems are usually made up of two or more materials. Special attention is given to magnetic impurities interacting with metallic contacts.
Studies have shown that when a metal has magnetic impurities, the electrons in the metal can form a screening cloud. The Kondo effect is a physical phenomenon that results in a cloud.
The Kondo cloud's behavior in normal systems is well- understood, but its properties in the presence of superconductivity have not yet been explored. Most physicists believe that the screening of spins in hybrid nanostructures takes place mostly in the screened phase, rather than in the unscreened quantum phase. Kondo clouds exist in both screened and unscreened quantum phases, according to researchers at the Budapest University of Technology and Economics in Hungary.
A correlated Kondo state can be formed in systems with a single spin S1/2 impurity attached to a metallic contact at sufficiently low temperatures, according to one of the researchers who carried out the study. A correlation cloud is formed around the impurity when it is in a state of spin screening.
Several researchers examined the properties of Kondo clouds, but only recently have teams started probing these systems. Ivan V. Borzenets and his colleagues at other institutions worldwide conducted one of the most notable experimental studies. The recent paper by Weymann and his colleagues sheds light on the behavior of Kondo clouds in superconductors.
"Understanding the spatial extension of various states is important to understand the fundamental aspects of strong electron correlations, which is relevant for various correlated materials," Weymann explained.
Weymann and his colleagues used state-of-the-art numerical and analytical renormalization group methods in their recent work. They were able to accurately predict the behavior of a Kondo cloud.
Weymann said that the system exhibits a quantum phase transition when the ground state changes between the Kondo state and the so-called Shiba state. It was thought that the screening happened in the Kondo phase. The Kondo cloud is also in the unscreened phase.
The results of the analyses and calculations carried out by this team of researchers show that the Kondo clouds have a characteristic jump at the quantum critical point. Their work could inform a series of experiments looking at the properties of Kondo clouds in superconductors.
Weymann said that they plan to extend their work to more complex systems.
Ctlin Pacu Moca and her colleagues wrote about Kondo Cloud in a Superconductor. There is a DOI titled "10.103/PhysRevLett. 127.186804".
The Kondo screening cloud was observed by Ivan V. Borzenets et al. There is a DOI of 10.1038/s41586-020-20586.
Nature and Physical Review Letters are in the journal.
The Science X Network will be launched in 2021.
A study predicts the behavior of a Kondo cloud in a superconductor.
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