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  • 1
    Electronic Resource
    Electronic Resource
    A simple theory of the Kondo hole : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5478-5480 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Kondo hole is an isolated nonmagnetic impurity in a heavy-fermion lattice. Experimentally, the Kondo hole can be realized by La or Th atoms replacing a Ce ion in a stoichiometric Ce compound or by Th impurities in a U–heavy-fermion system. Adding impurities to a Kondo lattice gradually destroys the coherence of the heavy-fermion ground state. Perturbations of the coherent state are conveniently studied in the f-electron density of states. We consider a dispersionless orbitally nondegenerate f band locally hybridized with one nearest-neighbor hopping tight-binding conduction band on a simple cubic lattice. A hybridization gap opens in the symmetric case, and the Kondo hole introduces a bound state in the gap. We study the effects of the scattering on the local density of f states in the neighborhood of the nonmagnetic impurity. The effects of the correlations within the f band are introduced via a self-energy, evaluated to second-order perturbation in U, using the d=∞ treatment of Schweitzer and Czycholl [Solid State Commun. 74, 735 (1990)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347971
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  • 2
    Electronic Resource
    Electronic Resource
    Local density of states in the vicinity of a Kondo hole : The 5th Joint MMM−Intermag Conference (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 5803-5805 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The substitution of magnetic ions by nonmagnetic impurities in a Kondo lattice gradually destroys the coherence of the heavy fermion groundstate. These nonmagnetic impurities are frequently referred to as Kondo holes. We consider a simple cubic Anderson lattice without orbital degeneracy and study the effects of the scattering off the Kondo hole in the local density of f states in the neighborhood of the nonmagnetic impurity. The correlations within the f band are introduced via a self-energy, evaluated to second order perturbation in U. We use the 1/d expansion method of Schweitzer and Czycholl to leading order (d=∞) in which the k integrations are properly carried out, but the k dependence of the self-energy is neglected. For a Kondo insulator we find a δ-function-like boundstate in the gap. The spectral weight of the boundstate decreases rapidly with increasing distance from the impurity. In the metallic case we obtain a resonance of finite width in the pseudogap of the lattice, which again is localized in the neighborhood of the Kondo hole. These states only appear in the coherent phase and disappear in the continuum at higher temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350142
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  • 3
    Electronic Resource
    Electronic Resource
    Correlated squeezed-state approach for the ground state of strongly correlated electrons coupled to local Holstein phonons (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 931-946 
    Details
    ISSN: 0392-6737
    Keywords: Phonons in crystal lattices ; Polarons and electron-phonon interactions ; Theories and models of superconducting state ; Nonclassical field states ; squeezed, antibunched, and sub-Poissonian states ; operational definitions of the phase of the field ; phase measurements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary In the present work we have applied the correlated squeezed-state approach to investigate the ground state of the extended Hubbard model which is coupled to local Holstein phonons. Our study begins with decoupling the electron and phonon subsystems approximately by introducing a variational correlated squeezed-state ansatz for the phonons. Then assuming the renormalized intersite electron correlation of the effective electronic Hamiltonian to be attractive and the renormalized on-site correlation repulsive, we have applied the generalized Hartree-Fock approximation to obtain the ground state of the system, which is a superconducting state with intersite pairing. With optimal values of the variational parameters the correlated squeezed-state approach will by construction yield a ground-state energy lower than those obtained in previous studies. This means that our variational ansatz is more stable as the ground state of the system. Furthermore, our variational study shows that in the correlated squeezed state the polaronic reduction effect of phonons is much more alleviated, and thus the mass enhancement inherent to the polaron effect is noticeably weakened. This weakening of the reduction effect should, in turn, significantly affect other physical properties of the system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02459075
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