Browsing by Author "Zhang, F. C."
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- 1/N expansion for the degenerate Anderson model in the mixed-valence regimeZhang, F. C.; Lee, T. K. (American Physical Society, 1983-07)The 1N expansion method for the degenerate Anderson model is formulated. N is the degeneracy factor of one of the f-electron configurations. Various ground-state properties are calculated. Excellent agreement with the result of Bethe ansatz for N=6 is shown. The rate of convergence of the series is analyzed. The merit and inadequacy of the method are discussed. At zero temperature the ratio of the magnetic susceptibility and the specific-heat linear coefficient is shown to lie within a range of 1 and 1+(N-1)-1.
- Extended and localized states in the periodic Anderson modelLee, T. K.; Zhang, F. C. (American Physical Society, 1986-12)The renormalized quasiparticle states are derived for a periodic Anderson model with a general hybridization matrix element between conduction electrons with two degrees of freedom and f electrons with N degrees of freedom. Only two out of N local f states form the extended quasi-particle bands while N−2 localized states remain. As an illustration we show that the self-energy due to the Kondo effect produces quasiparticle bands and a gap as obtained in the Kondo-boson approach.
- Hard-core repulsive interactions in even-parity electron pairings for heavy-fermion systemsZhang, F. C.; Lee, T. K. (American Physical Society, 1987-03)By studying the Anderson lattice Hamiltonian with spin-orbit coupling using an auxiliary boson method, we have examined the hard-core repulsive interactions in heavy-fermion materials. As a consequence of the anisotropy of the repulsive interaction, all lower-order partial-wave Cooper pairings in the even-parity channel are strongly impeded.
- A revised diagrammatic technique for the degenerate Anderson modelLee, T. K.; Zhang, F. C. (American Institute of Physics, 1984)The Goldstone diagrammatic technique developed by Keiter and Kimball for single impurity Anderson model is reformulated. Instead of having the self_energy functions defined on the real axis as the Brillouin_Wigner theory, we have defined the functions on the complex plane. This avoids the complicated and cumbersome regularization procedure required in the Keiter and Kimball formulation. Most important of all it makes the numerical calculations possible. The exact partition function may be written down in terms of irreducible self_energy diagrams. The Green function and spectral function are derived.
- Spectral density and magnetic susceptibility for the asymmetric degenerate Anderson modelZhang, F. C.; Lee, T. K. (American Physical Society, 1984-08)With the use of a new diagrammatic formulation, two coupled integral equations for the self-energy functions of the f hole and f particle in the asymmetric degenerate Anderson model are solved numerically. All the diagrams are included in the equations except the cross terms (or the vertex correction). The results for the spectral density function and the magnetic susceptibility show the scaling property described by the renormalization-group theory.
- Two competing interactions in the Anderson lattice modelZhang, F. C.; Lee, T. K.; Su, Z. B. (American Physical Society, 1987-04)The vertex function of the SU(N) Anderson lattice model is calculated by treating the intersite coupling perturbatively. There are two different scattering processes that contribute to the effective interactions. In one process the low-frequency Kondo resonance dominates and the effective interaction between quasiparticles is favorable for p-wave Cooper pairing at small values of kFR. In the other process all frequencies contribute and the effective interaction is against p-wave pairing for small kFR. This latter interaction is antiferromagnetic in nature.