Seminarium Fizyki Materii Skondensowanej

We study the temperature-dependent self-organization of magnetic moments coupled to itinerant electrons in finite-size low-dimensional nanostructures proximitized to a superconducting reservoir. At low temperatures, an effective Ruderman-Kittel-Kasuya-Yosida-type interaction between localized magnetic moments mediated by itinerant electrons leads to their helical ordering. This ordering in turn affects the itinerant electrons, inducing a topologically nontrivial superconducting phase that hosts Majorana end mods. Calculations show that the topological state can exist at least for a chain of magnetic atoms and for a ladder. It is interesting to note that in the case of a ladder, an unconventional topological phase transition with neither gap closing nor a change of symmetry is possible. This contradicts the common assumption that topological phase transitions in topological superconductors are accompanied by a closing of the topological gap or a change of the symmetry of the system.