Muon spin relaxation studies in strongly correlated electron systems

We describe recent progress of muon spin relaxation (μSR) studies in heavy-fermion (HF) and other strongly correlated electron systems. Measurements of the magnetic field penetration depth λ in HF superconductors UPt3, URu2Si2, UPd2Al3 and U2PtC2 have revealed that these systems are characterized by large ratios Tc/TF = 0.1−0.01 of Tc vs Fermi temperature TF derived from λ. This feature is common to high-Tc cuprate and other exotic superconductors. Zero-field μSR studies of magnetic order have elucidated a cross-over from spin glass ordering to nonmagnetic ground states in the ‘quadrupolar Kondo regime’ of (Y1−xUx)Pd3, and also suggested a possibility of incommensurate spin-density-wave (SDW) ordering in UNi2Al3.