The f electrons in rare earth and uranium intermetallic compounds usually possess magnetic and orbital degrees of freedom, and they often play essential roles in low-temperature magnetic properties through the couplings between the f electrons and their surroundings. In particular, an exchange interaction between the f and conduction electrons gives rise to many-body effects on both single-ionic sites (known as the Kondo effect) and inter-ionic sites (the Ruderman-Kittel-Kasuya-Yosida interaction: RKKY interaction). Although the former favors a paramagnetic ground state, the latter stabilizes long-range magnetic order. They may compete with each other, yielding an unusual many-body state of strongly correlated electrons. This electronic state, the so-called "heavy-fermion state", is recognized to be the evolution of Landau's Fermi-liquid quasiparticles with enhanced effective mass. Thus far, various new phenomena related to the heavy-fermion state have been discovered, including multipole order, unconventional superconductivity, and quantum critical behavior.
To investigate those phenomena, both macroscopic and microscopic measurements are indispensable. Our group has been using macroscopic and microscopic probes to examine the nature of quantum critical phenomena such as unconventional superconductivity, quantum spin fluctuation, and non-Fermi-liquid behavior.
