DYNAMICS OF VALENCE FLUCTUATING RARE EARTH COMPOUNDS (KONDO, VALENCE, FLUCTUATIONS)

This thesis reports on calculations of dynamical properties for valence fluctuating rare earth compounds based upon the degenerate Anderson Hamiltonian for magnetic impurities in metals. The main theme in this document is of the viability of the narrow many body "Kondo resonance" for providing a unifying account of the experimental results for valence fluctuators. Exploiting a recently developed self-consistent perturbation theory, numerical calculations have been made of (i) transport properties for Ce impurities in metals, (ii) finite temperature photoemission spectra for Ce and Yb valence fluctuating compounds, and (iii) magnetic relaxation rates for valence fluctuating Ce compounds. In reference to (i), a quantitative one parameter fit agrees over four temperature decades with the resistivity of Ce(,x)La(,1-x)B(,6), (ii) photoemission spectra calculated with only a change of hybridization strength qualitatively reproduce (alpha)-Ce and (gamma)-Ce data, and (iii) calculated magnetic relaxation rates reproduce the qualitative features of many valence fluctuators as well as an observed high temperature T(' 1/2) law. A rigorous calibration of the calculation method is provided by successful comparison of calculated thermodynamic quantities with exact Bethe Ansatz and Fermi Liquid theory results. The pathology known to exist for this self-consistent approach for low frequencies and temperatures is examined, and it is shown that many reliable results can be extracted despite the pathology. The possibility of phonon assisted conduction electron scattering into the 4f "Kondo resonance" is examined, and is shown to be capable of reproducing the scale of measured resistivity, thermopower, and infrared absorptivity of concentrated valence fluctuating systems, although the detailed agreement is less successful than for (i) through (iii) above. Finally, (a) some exact results for the transport properties of the related resonant level model are presented and compared with approximate memory function calculations and (b) a systematic numerical study of deviations from threshold behaviour in core-level x-ray photoemission spectra in metals is presented.