Interactions and Coherence in Lanthanide Metallic Compounds

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9501529 Fisk Technical Abstract: This project investigates a new intermetallic compound of ytterbium, indium, and copper, with physical properties which display a complex character and whose understanding would have major impact on the field of condensed matter physics. The compound has a first-order phase transition where the lattice constant and valence change discontinuously with no change in symmetry. Additional, novel thermodynamic properties are encountered in the series of compounds obtained by substitution of silver for indium. The principal investigators have succeeded in the difficult task of growing single crystals of these materials which will exhaustively characterized via resistivity, susceptibility, thermal expansion, elastic constants and neutron scattering as a function of temperature, pressure and magnetic field. The equation of state will be determined in an effort to understand the basis for the phase transition in terms of electronic and magnetic properties of these highly correlated electron, or "heavy fermion", materials. %%% Non-Technical Abstract: A small number of metals exhibit a property analogous to the condensation of a gas to a liquid: as the temperature is lowered below a critical temperature, the density changes discontinuously, with no change in crystal symmetry. There is an accompanying decrease in the strength of the magnetism of the metal. The investigators in this project have recently learned how to grow large crystals of a new intermetallic compound displaying the condensation behavior. The project involves a thorough investigation of the structure, magnetism, and electronic behavior of the compound and its alloys. The goal is to understand the nature of the interactions between electrons which drive the condensation, in particular there seems to be subtle interplay between the magnetism of the material and its cohesi ve energy. Such studies will improve our understanding of the conditions under which electrons in solids help to coherently bond the atoms in the crystalline state. The results may provide important information for the entire field of metal physics and magnetism.