The Kondo effect is one of the most important in quantum physics and describes the strange interference that magnetic atoms can have on metals. Typically, as metals cool, they become better conductors of electricity, because the reduction in energy means electrons can flow more smoothly. However, add one or two magnetic atoms and, below a certain temperature (the Kondo temperature), the electrical resistance starts to increase again. That’s the Kondo effect, and we already know a lot about it. But for the first time in physics, researchers from the California Institute of Technology (Caltech) and Yale University (USA) managed to precisely quantify the effect in a real material using fundamental physics calculations. The work, published in Science, represents an important step forward. Previously, scientists had to use real-world experiments and simplified models to pin down the Kondo effect, without getting predictions as accurate as the new method. Scientists have known about the Kondo effect since the 1930s: magnetic impurities can cause higher electrical resistance at lower temperatures. (Public domain) “It is now possible to predict the properties of some complicated materials solely by calculation without resorting to experiments,” says Caltech physicist Garnet Chan. Scientists already know what causes the Kondo effect. Electrons swarm around the magnetic impurities of the metal, canceling the magnetism of the atoms and at the same time preventing electrical flow. “That’s the signature of the Kondo effect, and it’s a property of the electrons in the impurity interacting with the electrons traveling through the bulk metal,” Chan says. However, knowing what is happening is not the same as being able to model it with complete precision. Such are the complexities of the electron interactions in this “many-body problem” that it is very difficult to predict when the resistance change will occur for different combinations of metals and magnetic impurities. Temperatures, electron spins, and magnetism interact at incredibly small scales in these materials as the Kondo effect takes hold. It is far beyond the capabilities of even the most powerful supercomputers. To overcome the challenges, the researchers took an ab initio (“from first principles”) approach. They borrowed techniques from chemistry to more completely model a single magnetic atom, without simplification, as if it were a larger molecule. With the help of some mathematical shortcuts and a lot of computer time, they applied the basic laws of quantum physics to this newly modeled magnetic atom, repeating the calculations over and over to narrow down their predictions. frameborder=”0″ enable=”accelerometer; autoplay; writing on clipboard; encrypted media; gyroscope; picture in picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” enablefullscreen> By comparing the modeling quantifications with laboratory measurements of the Kondo effect, the researchers demonstrated the high level of accuracy of their prediction system. In some cases, the new approach was 100 times more accurate than current simplified modeling. The researchers chose here the most basic examples of combinations of metals and magnetic atoms, but further down the line, there is the potential to study increasingly complex things. “These first materials that we have studied are like a small step, or a prototype problem, on the path to more complex phenomena such as high-temperature superconductors and quantum magnets,” says Chan. Better prediction methods mean that scientists can more confidently develop and research materials, such as superconductors, that promise to transform the systems we use for power grids and large-scale computing. The materials with the greatest potential tend to also have the most complex electronic behaviors, which is where the methods used in this study could still have a long way to go. do, but now that the approach has been shown to work, researchers can begin to expand it, giving scientists a tool to study complex behaviors of quantum materials without having to obtain laboratory data first. “We are in an exciting era in which faithfully predictive quantum descriptions of the full chemical complexity of real materials are within our reach,” says Caltech chemist Linqing Peng. The research has been published in Science. This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we take pride in our process, we are only human. If you spot an error, please let us know.
