Multi-orbital Anderson models and the Kondo effect: a NCA study enhanced by vertex corrections

Grewe, N.; Jabben, Torben; Schmitt, Sebastian

doi:10.1140/epjb/e2009-00064-0

Cited by 10 publications

(13 citation statements)

References 34 publications

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“…In this respect, it is also very effective and easily implemented to restrict the allowed local occupation and to exclude many-body states with very high excitation energies, as it was done for the two-orbital Anderson model (Ref. 22). …”

Section: Two-impurity Solver Based On Direct Perturbation Theorymentioning

confidence: 99%

Spectral properties of the two-impurity Anderson model with varying distance and various interactions

2012

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We present an approximation for the treatment of two interacting magnetic impurities immersed into a noninteracting metallic host. The scheme is based on direct perturbation theory with respect to the hybridization between the impurity and band electrons. This two-impurity enhanced noncrossing approximation can fully incorporate the indirect interactions between the impurities that are mediated by the conduction electrons as well as additional arbitrary direct interaction matrix elements. We qualify the approximation by investigating the uncoupled case and conclude that the two-impurity approximation is equally accurate as its single-impurity counterpart. The physical properties of the two-impurity Anderson model are first investigated in some limiting cases. In a regime where each of the uncoupled two impurities would exhibit a pronounced Kondo effect, we ignore the indirect coupling via the conduction band and only incorporate direct interactions. For a ferromagnetic direct exchange coupling, the system displays a behavior similar to a spin-one Kondo effect, while an antiferromagnetic coupling competes with the Kondo effect and produces a pseudogap in the many-body Kondo resonance of the single-particle spectral function. Interestingly, a direct one-particle hopping also produces a pseudogap, but additionally pronounced side peaks emerge. This gap is characteristically different from the case with antiferromagnetic coupling since it emerges as a consequence of distinct Kondo effects for the bonding and antibonding orbital, i.e., it reflects a splitting of even and odd parity states. For the general case of only indirect coupling via the conduction band, the results show signatures of all the previously discussed limiting cases as a function of the impurity-impurity distance. Oscillatory behavior in physical quantities is to be expected due to the generated Ruderman-Kittel-Kasuya-Yosida interaction. We are led to the conclusion that the well-known Doniach scenario captures essential aspects of this model, but the details, especially at small distances, are more complicated.

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Section: Two-impurity Solver Based On Direct Perturbation Theorymentioning

confidence: 99%

Spectral properties of the two-impurity Anderson model with varying distance and various interactions

2012

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“…which describe the low frequency susceptibilities very well. The form (38) corresponds to an exponential spin relaxation with relaxation time 1/Γ. The line-width Γ is directly proportional to the NMR impurity nuclear spinlattice relaxation rate Γ ∼ T 1 .…”

Section: Magnetic Susceptibilitymentioning

confidence: 99%

Dynamic susceptibilities of the single-impurity Anderson model within an enhanced noncrossing approximation

2009

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The single impurity Anderson model (SIAM) is studied within an enhanced non-crossing approximation (ENCA). This method is extended to the calculation of susceptibilities and thoroughly tested, also in order to prepare applications as a building block for the calculation of susceptibilities and phase transitions in correlated lattice systems. A wide range of model parameters, such as impurity occupancy, temperature, local Coulomb repulsion and hybridization strength, are studied. Results for the spin and charge susceptibilities are presented. By comparing the static quantities to exact Bethe ansatz results, it is shown that the description of the magnetic excitations of the impurity within the ENCA is excellent, even in situations with large valence fluctuations or vanishing Coulomb repulsion. The description of the charge susceptibility is quite accurate in situations where the singly occupied ionic configuration is the unperturbed ground state; however, it seems to overestimate charge fluctuations in the asymmetric model at too low temperatures. The dynamic spin excitation spectrum is dominated by the Kondo-screening of the impurity spin through the conduction band, i.e. the formation of the local Kondo-singlet. A finite local Coulomb interaction U leads to a drastic reduction of the charge response as processes involving the doubly occupied impurity state are suppressed. In the asymmetric model, the charge susceptibility is enhanced for excitation energies smaller than the Kondo scale TK due to the influence of valence fluctuations.

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“…We adopt the Kotliar-Ruckenstein formulation [49,50], which is convenient tool for discussing finite Coulomb interaction case and for analysis of effects introduced by polarization. Two other complementary methods used by us: equation of motion method (EOM) [51][52][53][54] and noncrossing approximation (NCA) [55][56][57][58][59][60] allow to get a deeper insight into the role of charge fluctuations in many-body physics and are better adopted for higher temperatures. EOM works in the whole parameter space except the close vicinity of Kondo fixed point but it breaks at low temperatures [53] and NCA gives reliable results in the wide temperature range, including the region close to T K and in the range of the lowest temperatures down to fraction of T K .…”

Section: Introductionmentioning

confidence: 99%

Kondo effect of a cobalt adatom on a zigzag graphene nanoribbon

2014

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Based on ab-initio calculations we discuss Kondo effect due to Co adatom on graphene zigzag nanoribbon. Co atom located at hollow site behaves as spin S = 1/2 impurity with d xz and d yz orbitals contributing to magnetic moment. Dynamical correlations are analyzed with the use of complementary approximations: mean field slave boson approach, noncrossing approximation and equation of motion method. The impact of interplay between spin and orbital degrees of freedom together with the effect of peculiarities of electronic and magnetic structure of nanoribbon on many-body resonances is examined. PACS numbers: 73.22.Pr, 73.23.-b, 75.20.Hr, 85.75.-d arXiv:1307.5872v1 [cond-mat.mes-hall]

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Multi-orbital Anderson models and the Kondo effect: a NCA study enhanced by vertex corrections

Cited by 10 publications

References 34 publications

Spectral properties of the two-impurity Anderson model with varying distance and various interactions

Spectral properties of the two-impurity Anderson model with varying distance and various interactions

Dynamic susceptibilities of the single-impurity Anderson model within an enhanced noncrossing approximation

Kondo effect of a cobalt adatom on a zigzag graphene nanoribbon

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