Russian scientists have discovered how magnons affect superconductivity.

The study has been published in the journal Physical Review B. Research related to the interplay between magnetism and superconductivity has a long and dynamic history, beginning with the initial discoveries of superconductors and ferromagnets. A significant milestone in this field was the discovery of so-called spin-split superconductivity — a quantum phenomenon resulting from the influence of ferromagnetic material or an external magnetic field on a superconductor. The presence of such a splitting in the density of states of the superconductor plays a crucial role, for instance, in the aforementioned giant spin-dependent Seebeck effect.

In recent years, scientists have focused on studying spintronics, where magnetism and superconductivity are combined to create new functional materials and devices with enhanced performance. Research in this area has reached a new level thanks to advancements in atomic and molecular physics, nanotechnology, and computational modeling.

However, for a long time, the impact of magnons on the superconducting density of states and the effect of quasiparticle hybridization remained insufficiently explored. The challenge of studying electron-magnon interactions in F/S heterostructures and their influence on spin-split density of states required in-depth analysis and new approaches.

To describe the interaction of electrons with magnons, researchers employed Green's function formalism and numerical methods. It turned out that spin-flip processes supported by magnons could reduce spin splitting and cause significant broadening of the quasiparticle spectrum branches. Under the influence of magnons, the density of states underwent substantial changes. External coherent peaks became broader, while internal peaks remained unchanged. This broadening, driven by magnon processes, is distinct from known mechanisms that affect all peaks, such as spin-orbit coupling or inelastic scattering on impurities. Additionally, numerical calculations were performed at different temperature values, allowing the tracking of the enhancement of the effect with an increase in the number of thermally excited magnons.

“The motivation for this work was an attempt to explain unusual experimental results. In the experiment by E. Strambini and colleagues, atypical behavior of the spin-split density of states in F/S structures was observed. It was previously assumed that the external peaks of this density of states should be higher than the internal ones. However, the results of E. Strambini and colleagues showed the opposite situation. We found that the electron-magnon interaction is what leads to this effect,” said Alexander Bobkov, a senior researcher at the Center for Advanced Methods in Mesophysics and Nanotechnology at MIPT. “The results of our work may aid in the development of ultra-sensitive detectors and efficient thermoelectric devices.”

The research conducted by Russian physicists, including a detailed analysis of the local density of states considering electron-magnon interactions, provides a deeper understanding of interactions in bilayer thin-film systems of ferromagnet-superconductor and contributes to the advancement of spintronic device development. The findings not only expanded the current understanding of what spin-split superconductivity might look like but may also serve as a foundation for new theoretical and experimental investigations in this field of science. The work was supported by the Russian Science Foundation.