Exotic Quantum States in Heavy Fermion Systems

Heavy fermion materials have served as a classical prototype of strongly correlated electron systems (SCES), where exotic quantum states emerge, such as anti-ferromagnetism, superconductivity and multipole ordering, due to the correlation effects between localized f and conduction electrons. Firstly, I will discuss the Cd-doping in the heavy fermion superconductor CeCoIn5, where spin-droplets are proposed to nucleate around the Cd-dopants due to quantum critical fluctuations, forming an inhomogeneous electronic state. Secondly, I will focus on the mysterious “hidden order” states in heavy-fermion materials URu2Si2 and PrFe4P12. Our point-contact spectroscopy results indicate a common Fermi surface gapping, which suggest the probable itinerant nature of the hidden multipolar ordering in the general context of dichotomy of localization and itineracy in f-electron systems.