ELECTRON-SPECTROSCOPY OF HEAVY-FERMION MATERIALS

The novel properties of heavy-fermion materials involve rare earth 4f electrons or actinide 5f electrons. For the 4f electrons the spectrum measured in photoemission and bremsstrahlung isochromat spectroscopies is dominated by single-site energetics and the impurity Anderson Hamiltonian gives at the semiquantitative level a unified description of the 4f spectrum and certain low energy properties characterized by a single-site Kondo temperature TK. Current efforts for 4f electron materials are directed at finding the quantitative limits of this impurity approach by detailed fitting of spectra using hybridization matrix elements calculated within the local density approximation (LDA). Examples presented herein are CeCu2Si2 and the α and γ phases of cerium metal. For the most commonly studied 5f case of uranium no such unified picture exists. Various current approaches to understanding uranium spectra include analysis and modeling of differences between measured spectra and LDA calculations, and purely experimental approaches such as alloy and dilution studies of UxY1-xPd3 and UxY1-xAl2. © 1990 IOP Publishing Ltd.