Interplay of superconductivity and magnetism in rare-earth nitride films

Superconductivity was given its name over 100 years ago because of its most obvious property: the loss of all electrical resistance below a certain critical temperature. This discovery was exciting, since it meant the possibility of energy transport without any losses. It took researchers over 20 years to realize that superconductors are more than just perfect conductors, they are also materials that expel magnetic fields, called perfect diamagnets. One direct consequence of this effect is the superconducting levitation, a magnet will hover over a superconductor without any visible support. Superconductivity is a rather fragile phase of matter, it will break down if a certain current limit is exceeded or if an applied magnetic field is too strong, and the material will become a normal conductor. For this reason it was believed that no magnetic material could become a superconductor at low temperatures. Even though there was a theoretical debate about the coexistence of the two states as early as in the 1950s, it was only in the 2000s that experimental evidence was found that some exotic uranium compounds are indeed superconducting ferromagnets. A very special and rare form of electron interaction, called triplet-pairing, makes it possible that a material can be both ferromagnetic and superconducting at the same time. We recently discovered that samarium nitride is likely one of those materials, and this research project is aimed at unraveling its unusual properties.