3,052 research outputs found
ESR OF A MAGNETIC PROBE IN THE NEIGHBORHOOD OF AN ANDERSON IMPURITY
No full text The renormalization group formalism was applied to calculate the spin lattice relaxation rate [Formula: see text] of a magnetic probe located in the neighborhood of a spin degenerate Anderson impurity. In the Kondo regime, [Formula: see text] as a function of the temperature T presents a peak at the Kondo temperature TK. For T≪TK, the system behaves as a heavy Fermi liquid, with an enhanced density of states, which increases with the decrease in the Kondo temperature; [Formula: see text] is a universal function of T/ΓK up to temperatures of the order of 100 ΓK, where ΓK is the Kondo width for temperatures lower than TK. The spin relaxation rate [Formula: see text] is proportional to the product of the magnetic susceptibility and temperature χT. Moreover, in the peak, [Formula: see text] at the Kondo temperature decreases with the increase in the distance between the Anderson impurity and the magnetic probe. </jats:p
Extended and localized states in the periodic Anderson model
No full textThe 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. © 1986 The American Physical Society.link_to_subscribed_fulltex
Spectral density and magnetic susceptibility for the asymmetric degenerate Anderson model
No full textWith 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. © 1984 The American Physical Society.link_to_subscribed_fulltex
Growth of laser host thin-film optical waveguides by pulsed laser deposition
No full textOptical waveguides of laser gain media are highly desirable because the high intensity-length product and good pump-signal mode overlap, which can be achieved in the waveguide geometry, leads to a reduced threshold pump power as compared to bulk lasers. Pulsed laser deposition (PLD) has emerged as a viable means of depositing epitaxial thin films of the correct composition. We report here the deposition of GGG and YGG thin films on YAG substrates and the deposition of sapphire on sapphire substrates
Effective models for the single impurity Anderson and Kondo model from continuous unitary transformations
No full textThe method of continuous unitary transformations (CUTs) is applied to the Anderson
impurity and the Kondo model aiming at the systematic derivation of convergent e ective
models. If CUTs are applied in a conventional way, diverging di erential equations
occur. Similar to poor mans scaling the energy scale, below which the couplings diverge,
corresponds to the Kondo temperature TK. We present a way to apply CUTs to the
Kondo and to the Anderson impurity model so that no divergences occur but a converged
e ective low-energy model is derived with small nite parameters at arbitrarily small energies.
The ground state corresponds to a bound singlet with a binding energy given by
the Kondo temperature TK
1N expansion for the degenerate Anderson model in the mixed-valence regime
No full textThe 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. © 1983 The American Physical Society.link_to_subscribed_fulltex
Spectral density for the Anderson\'s Model of two impurities.
No full textCalculamos a densidade espectral do modelo de Anderson de duas impurezas por meio de uma extensão do grupo de renormalização numérico (GRN) preservando a assimetria partícula-buraco do modelo. O estado fundamental deste modelo depende fortemente da competição entre a interação RKKY 1 e a temperatura de Kondo TK. Essa competição gera três regimes característicos: (i) 11\\ « k B TK, regime Kondo; (ii) - 1» kBTK, regime ferromagnético; and (iii) 1» kBTK, regime antiferromagnético. O Hamiltoniano é invariante sob inversão das coordenadas da impureza ± R/2. Seus auto-estados, portanto, podem ser classificados de acordo com a paridade. Calculamos as densidades espectrais par e ímpar para os parâmetros representativos do modelo em cada um dos três regimes mencionados acima. Várias características dos resultados numéricos, associadas com a formação de um tripleto ou singleto entre as impurezas e com o efeito Kondo, são discutidas.We calculated the spectral density for the two-impurity Anderson model by means of an extension of the numerical renormalization-group (NRG) preserving the particle-hole asymmetry of the model. The ground state of this model depends strongly on the competition between the RKKY interaction I and the Kondo temperature TK. That competition generates three characteristic regimes: (i) 11\\« kBTK, Kondo regime; (ii) - I» kBTK, ferromagnetic regime; and (iii) I > > k B TK, antiferromagnetic regime. The Hamiltonian is invariant under inversion of the impurity coordinates ± R/2 . Its eigenstates can therefare be classified according to parity. We have calculated the even and odd spectral densities for model parameters representative of each of the three above mentioned regimes. Various features af the numerical results, associated with the formation of an impurity singlet ar triplet and with the Kondo effect, are discussed
Spectral density for the Anderson\'s Model of two impurities.
No full textCalculamos a densidade espectral do modelo de Anderson de duas impurezas por meio de uma extensão do grupo de renormalização numérico (GRN) preservando a assimetria partícula-buraco do modelo. O estado fundamental deste modelo depende fortemente da competição entre a interação RKKY 1 e a temperatura de Kondo TK. Essa competição gera três regimes característicos: (i) 11\\ « k B TK, regime Kondo; (ii) - 1» kBTK, regime ferromagnético; and (iii) 1» kBTK, regime antiferromagnético. O Hamiltoniano é invariante sob inversão das coordenadas da impureza ± R/2. Seus auto-estados, portanto, podem ser classificados de acordo com a paridade. Calculamos as densidades espectrais par e ímpar para os parâmetros representativos do modelo em cada um dos três regimes mencionados acima. Várias características dos resultados numéricos, associadas com a formação de um tripleto ou singleto entre as impurezas e com o efeito Kondo, são discutidas.We calculated the spectral density for the two-impurity Anderson model by means of an extension of the numerical renormalization-group (NRG) preserving the particle-hole asymmetry of the model. The ground state of this model depends strongly on the competition between the RKKY interaction I and the Kondo temperature TK. That competition generates three characteristic regimes: (i) 11\\« kBTK, Kondo regime; (ii) - I» kBTK, ferromagnetic regime; and (iii) I > > k B TK, antiferromagnetic regime. The Hamiltonian is invariant under inversion of the impurity coordinates ± R/2 . Its eigenstates can therefare be classified according to parity. We have calculated the even and odd spectral densities for model parameters representative of each of the three above mentioned regimes. Various features af the numerical results, associated with the formation of an impurity singlet ar triplet and with the Kondo effect, are discussed
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