R. Jullien

Theory of Kondo lattice

In order to understand the low temperature anomalous properties of some rare‐earth compounds (such as CeAl2, CeAl3, TmSe), we introduce a Kondo lattice hamiltonian in which a localized 1/2 spin per site interacts antiferromagnetically with the conduction electron spins. We investigate the ground state properties of this hamiltonian by using a real space renormalization group method. After studying a simpler one dimensional analog we study the original hamiltonian in one dimension when there is one conduction electron per site.

Thermal dependence of the neutron diffraction quasi-elastic line width in anomalous rare-earth compounds: A spin fluctuation theoretical model

Abstract A spin-fluctuation model involving a narrow 4f band with a strong exchange-enhancement factor is developed to account for the temperature dependence of the neutron quasi-elastic linewidth and good agreement is found with experiments in anomalous rare-earth compounds.

Resistivity of the Anderson lattice: Application to TmSe

Abstract The resistivity of the “Anderson lattice” is computed for the antiferromagnetic ordering and a good agreement is found for the case of TmSe if an insulating phase is assumed for the perfectly stoichiometric TmSe compound.

Properties of the periodic Anderson Hamiltonian: Calculations on finite cells

We present calculations for the ground state and the lowest excited states of the one‐dimensional periodic Anderson Hamiltonian with two electrons per site and arbitrary magnitude of the repulsion parameter U. We present exact numerical results for finite cells (up to N = 4) and introduce ’’modified’’ periodic boundary conditions to facilitate the extrapolation for larger N. The lowest energy excitations for adding or subtracting an electron show that the system is insulating, and the lowest spin‐flip excitations indicate a near instability to antiferromagnetism due to the ’’nesting’’ of the Fermi surface in 1d. For N = 4 the results agree well with infinite cell calculations both for small U and for large U in the Kondo lattice limit. The primary results are the continuous variation from the U = 0 to the Kondo lattice and mixed valence regimes and the importance of correlations, omitted in the impurity calculations, which lead to an insulating gap and dispersion in the electronic and magnetic excitations.

Theoretical Models for Narrow Band Effects in Rare Earths and Actinides

We review here some theoretical approaches able to describe the properties of anomalous rare-earth (Ce, Yb…) metals, alloys and compounds or of actinide metals and compounds; in the second case, we emphasize the case of nearly magnetic metals (Np, Pu) or compounds (UAl2, NpRh3…).