The f electrons in rare earth and uranium intermetallic compounds typically possess both magnetic and orbital degrees of freedom, playing crucial roles in low-temperature magnetic properties through their interactions with the surrounding environment. Notably, the exchange interaction between f electrons and conduction electrons leads to many-body effects at both single-ionic sites (known as the Kondo effect) and inter-ionic sites (the Ruderman-Kittel-Kasuya-Yosida interaction, or RKKY interaction). While the Kondo effect tends to favor a paramagnetic ground state, the RKKY interaction promotes the stabilization of long-range magnetic order. These two interactions may compete with one another, resulting in a unique many-body state characterized by strongly correlated electrons. This electronic state, referred to as the heavy-fermion state, is understood as the evolution of Landau's Fermi-liquid quasiparticles, which possess strongly enhanced effective mass. To date, various new phenomena associated with the heavy-fermion state have been identified, including multipole order, unconventional superconductivity, and quantum critical behavior.
To investigate these phenomena, both macroscopic and microscopic measurements are essential. Our research group has employed a combination of macroscopic and microscopic probes to explore the nature of quantum critical phenomena, such as unconventional superconductivity, quantum spin fluctuations, and non-Fermi-liquid behavior.
