RKKY interaction and coexistence with magnetism in superconducting systems

Abstract

When cooled down, the electrical resistivity of certain materials suddenly drops to zero at some specific temperature. This phenomenon is called superconductivity. As we are living in a world steadily demanding more energy, being able to prevent energy loss by transferring electrical currents through superconducting wires would be a huge advantage. Unfortunately, superconductivity normally sets in at quite low temperatures. Applications are therefore limited to cases where the benefit of superconductivity outweighs the cost of cooling down the material. Still, superconductors are, for example, used to make the strong magnetic fields that are needed in MRI devices, helping patients in hospitals. Superconductors can also be useful for spin-based electronics where information is stored and transported using the electron spin, rather than the electron charge. Spin-based electronics seeks to make electronic devices smaller and faster, while wasting less energy than normal charge-based electronics. Combining superconductivity and spin-based electronics does, however, require combining superconductivity with magnetism. Although interesting phenomena can arise when superconductivity and magnetism meet, this can also be problematic as superconductors and magnets are natural enemies: Superconductors normally expel any magnetic fields applied to them and lose their superconducting properties when the applied field becomes too large. This thesis provides an introduction to four research papers exploring interplay between superconductivity and magnetism. The magnetism is introduced through application of magnetic fields to superconductors or by placing superconductors next to magnetic materials. The articles investigate both interesting phenomena that can arise in such system, with possible applications within spin-based electronics, and how superconductors can be designed to withstand larger magnetic fields.