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1.
Y. Tao G. Bergmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(1):42
The Friedel oscillations in the vicinity of a Friedel-Anderson (FA) impurity are investigated numerically. For an FA impurity
in the local moment limit the normalized amplitude A(ξ) is S-shaped, approximately zero at short distances, approaching two at large distances and crossing the value one at the
characteristic length ξ
1/2. Surprisingly, the Friedel oscillations of a simple non-interacting Friedel impurity with a narrow resonance at the Fermi
level show a very similar behavior of their amplitude A(ξ). A comparison correlates the resonance width and the Kondo energy of the FA impurity with the characteristic length ξ
1/2 of the Friedel oscillations. 相似文献
2.
The dependence of the superconducting transition temperature Tc on Ce impurity concentration and the specific heat jump at Tc as a function of Tc are reported for the system (Ce)Sn3. The experimental results are analyzed using a theory due to Kaiser concerning the effect on superconductivity of nonmagnetic localized resonant impurity states This analysis yields values for the intraatomic Coulomb repulsion parameter Ueff and the Ce local density of states at the Fermi level N? (EF). The results of low temperature normal state heat capacity and magnetic susceptibility measurements which give independent estimates of N? (EF) are also reported. A large pressure dependence of the Tc of (Ce)Sn3 alloys was observed for pressures up to 20 kbar. This behavior is similar to that previously observed in several other superconducting matrix-Ce impurity systems in which the Ce solute 4f electron shell undergoes a continuous-pressure induced demagnetization. 相似文献
3.
K. H. Fischer 《Zeitschrift für Physik B Condensed Matter》1981,42(1):27-38
We investigate the influence of the Kondo effect on the electrical resistivity of spin glasses. Our approximation reduces in the limit of vanishing impurity concentrations to the Suhl-Nagaoka theory for the Kondo effect. The magnetic impurity interactions are taken into account in the form of time dependent two-spin correlation functions which can be measured by neutron scattering. The dynamics of the impurity spins leads to a partial destruction of the Kondo effect. For the resistivity this can be described by a temperature dependent effective spinS
eff
2
(T) withS
eff
2
0 forT0 andS
eff
2
S(S+1) forT, and by a reduction of the Kondo temperatureT
K. Sufficiently strong interactions lead toT
K=0. We obtain a resistivity maximum at a temperatureT
m due to the interplay of the Kondo effect and the spin dynamics;T
m depends onT
K and on the excitation spectrum, and therefore on parameters such as impurity concentration or pressure. The ratioT
m/Tf (T
f is the freezing temperature) is calculated for a single relaxation time and for a square density of relaxation modes and is compared with experimental data forAuCr,AuMn,AgMn, andCuMn. The influence of other possible modes on various spin glass properties is discussed.SFB 125 Aachen-Jülich-Köln 相似文献
4.
This review considers the experimental and theoretical studies of concentrated Kondo systems (CKS), Kondo lattices, substitutional solid solutions and their transition from Kondo impurity to Kondo lattice, and ‘intermediate valence compounds’ which are, in fact, high T K CKS (T K is the Kondo temperature). The anomalous low temperature properties of CKS are related to the formation of the narrow (~k B T K) high-amplitude Abrikosov-Suhl resonance E R in the vicinity of the Fermi level E F. This resonance is situated exactly at E F in low T K CKS with T K < ΔCF and near E F in high T K CKS with T K > ΔCF (ΔCF is the crystal field splitting). In low T K ‘j=1/2’ CKS the condition E R=E F leads to an increase of the density of states at E F, which is large enough to induce heavy fermion superconductivity in CeCu2Si2, UBe13. We demonstrate that the transition from low T K (E R=E F) to high T K CKS (E R≠E F) might be what was formerly considered as a ‘Kondo-lattice-intermediate valence state’ transition. It appears that in many cases the essentially non-integer valence state of the rare-earth elements in metallic compounds is thermodynamically unstable with respect to a transition to an almost integer valence state, because it realizes the maximum gain in free energy from the Kondo condensation. 相似文献
5.
M. N. Kiselev A. S. Mishchenko 《Journal of Experimental and Theoretical Physics》1998,86(5):1008-1019
A self-consistent microscopic theory of the relaxation of the crystal-field levels of an impurity ion in a state with an integer
valence implanted in a normal metal is devised. A microscopic approach based on the Coqblin-Schrieffer-Cooper approach, rather
than the formal model of the sf exchange interaction, makes it possible to take into account the specific details of both the crystal-field states of the
impurity ion and the electronic band spectrum of the metal. A new method for the soft spectroscopy of electronic states based
on measurements of the temperature dependence of the width ΓMM′(T) of transitions between the crystal-field states |M〉 of a paramagnetic ion implanted in the compound being studied is proposed. To make specific use of this method in neutron
and optical spectroscopy, a classification of the types of temperature dependence of the natural relaxation width γ
M
(T) of the levels is devised, and procedures for possible experimental methods are proposed. A nonzero value of the natural
relaxation width γ
G
(T) of the crystal-field ground state | G〉 of an impurity ion at zero temperature is obtained within the proposed self-consistent
model, but is beyond the scope of perturbation theory. It is shown that the widely accepted estimate of the characteristic
temperature of Kondo systems T*=Γ
G(T=0)/2 from the quasielastic scattering width at zero temperature Γ
G
(T=0)/2 is incorrect in the case of strong relaxation in a system with soft crystal fields. The proposed model is applied to
the quantitative analysis of the relaxation of the crystal-field levels of paramagnetic Pr3+ ions implanted in CeAl3 and LaAl3. The results of the calculations are in quantitative agreement with the experimental data.
Zh. éksp. Teor. Fiz. 113, 1843–1865 (May 1998) 相似文献
6.
Professor Dr. Toshio Soda 《Zeitschrift für Physik B Condensed Matter》1971,14(1):55-77
A magnetic impurity, having the s-j interaction with conduction electrons, under the crystalline field of host metals is investigated. The Hamann integral equation for the t-matrix can be derived and solved by the method of Zittartz and Müller-Hartmann for the cases of (1) small splittings, yielding the Kondo anomaly and decrease of the Kondo temperatureT K compared with no splittings, (2) a large splitting from the crystalline ground doublet state, producing the higherT K by the exicited level, and (3) a large splitting from the ground singlet state giving no Kondo effect. The macroscopic properties are calculated for (1) and (2). 相似文献
7.
The intersite contribution to the ground state energy for the two impurity Anderson model is calculated to first order in 1/N. The dependence of this contribution on the interimpurity separation has an R?1 or R?3 envelope for distances smaller or larger than a length νF/TA ranges from a value equal to the bare ?-level position (in the weak valent regime) to the Kondo temperature (in the local moment limit). 相似文献
8.
Yu. N. Ovchinnikov A. M. Dyugaev 《Journal of Experimental and Theoretical Physics》1999,88(4):696-709
The magnetic field dependence of the average spin of a localized electron coupled to conduction electrons with an antiferromangetic
exchange interaction is found for the ground state. In the magnetic field range μH∼0.5T
c
(T
c
is the Kondo temperature) there is an inflection point, and in the strong magnetic field range μH≫T
c
, the correction to the average spin is proportional to (T
c
/μ H)2. In zero magnetic field, the interaction with conduction electrons also leads to the splitting of doubly degenerate spin
impurity states.
Zh. éksp. Teor. Fiz. 115, 1263–1284 (April 1999)
Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor 相似文献
9.
The formation of deeply-bound antikaonic nuclear states in nuclear (K−,N) reactions is investigated theoretically within a distorted-wave impulse approximation (DWIA), considering the isospin properties of the Fermi-averaged elementary amplitudes. We calculate the formation cross sections of the deeply-bound states by the (K−,N) reactions on the nuclear targets, 12C and 28Si, at incident K− lab momentum pK−=1.0 GeV/c and θlab=0°, introducing a complex effective nucleon number Neff for unstable bound states in the DWIA. The results show that the deeply-bound states can be populated dominantly by the (K−,n) reaction via the total isoscalar ΔT=0 transition owing to the isospin nature of the amplitudes, and that the cross sections described by ReNeff and ArgNeff enable to deduce the structure of the nuclear states; the calculated inclusive nucleon spectra for a deep -nucleus potential do not show distinct peak structure in the bound region. The few-body and states formed in (K−,N) reactions on s-shell nuclear targets, 3He, 3H and 4He, are also discussed. 相似文献
10.
Gorazd Cveti
Alexey Yu. Illarionov Bernd A. Kniehl Anatoly V. Kotikov 《Physics letters. [Part B]》2009,679(4):350-354
Using the leading-twist approximation of the Wilson operator product expansion with “frozen” and analytic versions of the strong-coupling constant, we show that the Bessel-inspired behavior of the structure function F2 and its slope ∂lnF2/∂ln(1/x) at small values of x, obtained for a flat initial condition in the DGLAP evolution equations, leads to good agreement with experimental data of deep-inelastic scattering at DESY HERA. 相似文献
11.
Using a novel slave boson mapping, which was recently proposed by us for two Anderson impurities embedded in a metal, we present here spectral functions for all pseudoparticles involved in the mapping. These were numerically calculated in the framework of the Non-Crossing Approximation for different temperatures and inter-impurity distances, both for the degenerate (Nf = 6) and nondegenerate (Nf = 2) models. For the nondegenerate case, temperature dependencies of the partial occupancies and the spin-spin correlation function suggest that an antiferromagnetic (AFM)-like ground state is formed at suitable inter-impurity separation. By contrast, Kondo quenching of the impurity moments takes place for the isotropic Nf = 6 case even when a direct AFM interaction is introduced in order to amplify the indirect (inherent) one. Numerical calculations are in agreement with our previous prediction [Phys. Rev. B 47, 14,297 (1993)] that no AFM-like ground state can appear for two isotropic degenerate impurities. 相似文献
12.
We use the variational method to investigate the ground state phase diagram of the Kondo lattice Hamiltonian for arbitraryJ/W, and conduction electron concentrationn
c (J is the Kondo coupling andW the bandwidth). We are particularly interested in the question under which circumstances the globally singlet (collective Kondo) Fermi liquid type ground state becomes unstable against magnetic ordering. For the collective Kondo singlet we use the lattice generalization of Yosida's wavefunction which implies the existence of a large Fermi volume, in accordance with Luttinger's theorem. Using the Gutzwiller approximation, we derive closed-form results for the ground state energy at arbitraryJ/W andn
c, and for the Kondo gap atn
c=1. We introduce simple trial states to describe ferromagnetic, antiferromagnetic, and spiral ordering in the small-J (RKKY) regime, and Nagaoka type ferromagnetism at largeJ/W. We study three particular cases: a band with a constant density of states, and the (tight binding) linear chain, and square lattice periodic Kondo models. We find that the lattice enhancement of the Kondo effect, which is described in our theory of the Fermi liquid state, pushes the RKKY-to-nonmagnetic phase boundary to much smaller values ofJ/W than it was previously thought. In our study of the square lattice case, we also find a region of itinerant, Nagaoka-type ferromagnetism at largeJ/W forn
c 1/3. 相似文献
13.
The effective atomic number (Zeff) and effective electron density (Neff) of eight heavy metal oxide (HMO) glasses have been determined using the Monte Carlo simulation code MCNP for the energy range of 10?keV–10?MeV. The interpolation method was employed to extract Zeff and Neff values from the simulation and that calculated with the help of XCOM program. Comparisons are also made with predictions from the Auto-Zeff software in the same energy region. Wherever possible, the simulated values of Zeff and Neff are compared with experimental data. In general, a very good agreement was noticed. It was found that the Zeff and Neff vary with photon energy and do not have extended intermediate regions where Compton scattering is truly dominating; only dips slightly above ~1.5?MeV were recorded. Zeff and Neff are found to increase with PbO and Bi2O3 contents. It was found that the Zeff value rather than the Neff value is a better indicator for PbO and/or Bi2O3 contents. 相似文献
14.
T. S. Altshuler A. E. Altshuler M. S. Bresler 《Journal of Experimental and Theoretical Physics》2001,93(1):111-116
An EPR study of ytterbium dodecaboride (YbB12) showed the presence of an energy gap with a width of 2Δ=12 meV in the energy spectrum of this Kondo insulator. The temperature dependence of the energy gap was determined by interpreting the experimental data within the framework of the exciton dielectric model: Δ(T)=72 K at an absolute zero and Δ(T)=0 at ~115 K. The temperature dependence of the EPR line-width exhibits a feature at 13–15 K, which is indicative of a finite density of states inside the gap. This can be related to the presence of impurity states or bound polaron excitations in the electron spectrum of YbB12. 相似文献
15.
The transmission properties of one-dimensional (1D) photonic crystals containing two kinds of single-negative (ENG and MNG) material are investigated theoretically. A type of photonic gap with zero effective phases (zero-φeff) and the effects of absorption on the properties of the zero-φeff gap were shown. Specifically, it is demonstrated that strong absorption creates photon states inside the gap and this makes the band gap to be of zero width. 相似文献
16.
Summary Using the Lanczos scheme (tridiagonalization) we investigate the impurity contribution to the single-impurity Kondo model.
This is accomplished by obtaining the ground-state energy of aN-particle system and a (N+1)-particle system, and obtaining the functional dependence ofg(J) (whereJ is the strength of the interaction). Hereg(J) is the coefficient of a correction term which is of order 1/N. The density of states at the Fermi level is effectively changed by the factorg(J). The excess heat capacity associated with the impurity is then proportional tog(J).
To speed up publication, the authors of this papers have agreed to not receive the proofs for correction. 相似文献
17.
18.
A. CALLEGARI R. PEARMAN SUSAN CHOI PETER ENGELS H. SRIVASTAVA M. GRUEBELE 《Molecular physics》2013,111(4-5):551-568
The threshold region of vibrational energy redistribution (IVR) presents a great experimental and computational challenge for organic molecules with more than 10 degrees of freedom. The density of states ρtot is high and requires high resolution measurements over a wide range to cover all relevant timescales experimentally. Yet ρtot is sufficiently low that IVR quantities like the initial relaxation time τIVR or the number of participating states Neff are very sensitive to the coupling structure. To highlight the competing effects of molecular symmetry and mode localization on the accessible density of states, this work complements a study of benzene (Callegari, A., Merker, U., Engels, P., Srivastava, H. K., Lehmann, K. K., and Scoles, G., 2000, J. chem. Phys., 113, 10583) by measuring the CH overtone spectra of pyrrole (C4H4NH) and 1,2,3-triazine (C3N3H3) using eigenstate-resolved double-resonance spectroscopy. Large scale computations of IVR dynamics were undertaken, applying filter diagonalization to analytically fitted fourth-order ab initio force fields. With an overall adjustment to the anharmonicity of the potential, the modelled Neff and τIVR agree with the experimental quantities within a factor of 2 to 3, which is reasonable for a rate theory in the threshold regime. The models also correctly predict the experimentally observed trends of τIVR and Neff for the two molecules, and provide insight into the highly off-resonant coupling mechanism, which yields very sharp linewidths. 相似文献
19.
E. Bauer N. Pillmayr E. Gratz G. Hilscher D. Gignoux D. Schmitt 《Zeitschrift für Physik B Condensed Matter》1987,67(2):205-210
The temperature dependence of the electrical resistivity, thermopower, specific heat, susceptibility and magnetization of CeCuAl3 are presented. CeCuAl3 behaves as a Kondo lattice system with antiferromagnetic ground state properties (T
N
2.8 K). The valency of Ce in this tetragonal compound is close to 3 and the overall crystal field splitting found from our results is about 150 K. The Kondo temperatureT
K
in the crystal field ground state, estimated from the magnetic susceptibility and the specific heat, is of the order of 8 K. 相似文献
20.
A one-dimensional diagonal tight binding electronic system with dichotomic correlated disorder in the presence of external
d.c field is investigated. It is found numerically that the conductance distribution obeys fairly well to log-normal distribution
in weak disorder strength in localized regime, which indicates validity of single parameter scaling theory in this limit.
Contrary to the universal cumulant relation C
1 = 2C
2 in the absence of d.c. field, we demonstrated numerically that C
1 ≫ 2C
2 in the presence of the field in localized regime. We interpret this result as suppression of the fluctuation effects by the
external field. In addition, it is obtained that the quantity NF
c
, here N is the system size and F
c
is the crossover field, decreases as the as the system energy E increases. Moreover, we find numerically a simple linear relation between the average logarithm of the conductance 〈ln(g)〉 and the field strength as 〈ln(g)〉 = C(N, λ)F, here C(N, λ) is a constant for particular values of N and λ, which is the Poisson parameter of the dichotomic process. 相似文献