UC Berkeley

Many-body systems present some of the deepest challenges in physics. The interactions between a large number of objects can give rise to phenomena which are unprecedented from the standpoint of the individual objects themsleves. In many-body quantum systems, such as the electron fluid in metals, an effective single-particle description for modeling their properties has been successfully developed and tested. One of the central open questions in the study of many-body quantum physics lies in systems where the particles interact with each other strongly enough that the conventional description in terms of effectively individual particles fails. This problem is prevalent in metals which are on the verge of magnetism -- for example, when perturbed by external stress, magnetic field, or electric field, they spontaneously become magnetic. Notably, some of these metals achieve superconductivity, a collective electron phase which exhibits zero electrical resistance, at remarkably high temperatures. This text focuses on experimentally addressing fundamental open questions regarding strongly-interacting electrons in such metals. It is divided into separate sections on nearly-antiferromagnetic iron-based superconductors, a novel layered ferromagnetic superconducting compound, and a cerium-based alloy hosting an interplay between magnetism and the spontaneous localization of electrons to their host atoms.