f-f Magnetic polaron Wigner glass and anomalous superconductivity in U1-xThxBe13

Mechanisms of the anomalous properties in the heavy fermion superconductor UBe1,3 and its alloys, in particular for the Th dopings, are studied in det ail based on the fundamental electronic states to be consistent with all th e crucial experimental results. As the reference systems for the magnetic p olaron formation, Ce monopnictides, as well as USb and UTe, are mentioned. From detailed systematic studies of the dilute alloy systems, it is postula ted that the 5f states in UBe13 split into the well-localized core 5f Gamma (7)(2) singlet state and other delocalized 5f slates situated around the Fe rmi energy forming the f-f magnetic polarons through the strong intra-atomi c ferromagnetic f-f exchange interaction. The accompanied lattice polarons are also shown to play important roles. In the p-d band states, the f-f exc hange interaction and the intersite p-f mixing interactions for the p-f Kon do state are of nearly equal strengths causing a rich variety of delicately balanced states. For the p-f Kondo state, the polarization of the core Gam ma(7)(2) state through the f-f exchange interaction causes novel Kondo effe ct different from that in Ct compounds. At higher temperatures above 50 K. the conventional Kondo singlet through the p-f mixing dominates. Below 5 It , the f-f magnetic polarons form amorphous types of Wigner crystallization, or Wigner glass. and the p-d band states are strongly scattered forming ps eudolocalized stares, in particular below the Fermi energy. The complicated unusual anomalies in UBe1,3 and its alloys originate fundamentally in the above delicate balance. The anomalous superconducting state was identified as the s-wave pairing through the strong charge fluctuation of the Wigner g lass and occurs in competition with the magnetic polaron and the pseudoloca lized states with a strongly reduced T-c due to the large resistivity at 7, causing 3 double peak structure of T-c as a function of Th doping, as well as unusual characteristics of the temperature dependence of H-c2. In gener al, the Wigner glass state persists even in the superconducting state stayi ng in the normal state causing unusual bulk superconducting state. (C) 2000 Elsevier Science B.V. All rights reserved.