A quantum mystery that had puzzled physicists for decades has been solved

Physicists from the California Institute of Technology and Yale University have learned to precisely calculate the Kondo effect — a phenomenon in which magnetic impurities cause the resistance of a metal to increase upon cooling. The new approach accounts for the real structure of the material, not just its simplified model. The work has been published in the journal Science.

Normally, cooling helps a metal conduct electricity: thermal motion weakens, making it easier for electrons to move. However, even a small admixture of magnetic atoms changes the picture. At sufficiently low temperatures, resistance stops decreasing and begins to increase.

Physicists already know the reason for this behavior: conduction electrons interact with the magnetic impurity and screen its magnetic moment. It is far more difficult to predict at what temperature the effect will manifest in a specific material. This requires accounting for the interrelated behavior of many electrons.

The authors applied quantum chemistry methods developed for describing molecules. These allowed them to calculate in detail the electronic structure of the impurity atom inside the metal and then determine the characteristics of the resulting quantum state.

The method was tested on seven transition metals whose atoms were embedded in copper. For most of the studied impurities, the accuracy of predictions significantly surpassed the results of previous model calculations — in some cases by roughly two orders of magnitude. The obtained values were compared with experimental data.

So far, the approach has been tested on relatively simple systems. In the future, it may help study more complex quantum materials, including high-temperature superconductors. The main achievement of the work is the ability to derive the properties of a specific substance from fundamental laws, taking into account its chemical composition.