Electron spectrum and stability of the saturated ferromagnetic state in a Hubbard model with strong correlations

Zarubin, A. V.; Irkhin, V. Yu.

doi:10.1134/1.1130914

Cited by 12 publications

(19 citation statements)

References 28 publications

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“…The Gutzwiller variational approach [42] gives only the critical concentration of saturated ferromagnetic state n 2 = 0.68 for sc-and bcc-lattices. Our results also agree with the results obtained by the expansion of one-particle Green's functions over the inverse coordination number [43]. In the case of "tunable" DOS with the peak near the band-edge we have n 1 = 0.20 and n 2 = 0.31 at a = 0.3, n 1 = 0.09 and n 2 = 0.15 at a = 0.15.…”

Section: Ferromagnetic Ordering In the Modelsupporting

confidence: 90%

Electron correlations in narrow energy bands: modified polar model approach

Didukh¹,

Skorenkyy²,

Kramar³

2008

Condens. Matter Phys.

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The electron correlations in narrow energy bands are examined within the framework of the modified form of polar model. This model permits to analyze the effect of strong Coulomb correlation, inter-atomic exchange and correlated hopping of electrons and explain some peculiarities of the properties of narrow-band materials, namely the metal-insulator transition with an increase of temperature, nonlinear concentration dependence of Curie temperature and peculiarities of transport properties of electronic subsystem. Using a variant of generalized Hartree-Fock approximation, the single-electron Green's function and quasi-particle energy spectrum of the model are calculated. Metal-insulator transition with the change of temperature is investigated in a system with correlated hopping. Processes of ferromagnetic ordering stabilization in the system with various forms of electronic DOS are studied. The static conductivity and effective spin-dependent masses of current carriers are calculated as a function of electron concentration at various DOS forms. The correlated hopping is shown to cause the electron-hole asymmetry of transport and ferromagnetic properties of narrow band materials.

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Section: Ferromagnetic Ordering In the Modelsupporting

confidence: 90%

Electron correlations in narrow energy bands: modified polar model approach

Didukh¹,

Skorenkyy²,

Kramar³

2008

Condens. Matter Phys.

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“…The spectral density approximation (SDA) [27,28] gives the following results: n 1 = 0.34, n 2 = 0.68 for sc lattice and n 1 = 0.52, n 2 = 0.68 for bcc lattice. Our results for bcc lattice are n 1 = 0.55 and n 2 = 0.64 and also agree with paper [29]. In the case of "tunable" DOS with a peak near the band-edge we have n 1 = 0.20 and n 2 = 0.31 for a = 0.3, n 1 = 0.09 and n 2 = 0.15 for a = 0.5.…”

Section: Ferromagnetic Ordering In the Model: The Influence Of Dos Formsupporting

confidence: 80%

Mott Transition, Ferromagnetism and Conductivity in the Generalized Hubbard Model

et al. 2007

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The electron correlations in narrow energy bands are examined within the framework of the Hubbard model, generalized by taking into account the correlated hopping of electrons. Electronic conductivity and ferromagnetic ordering stabilization in the system with various forms of electronic density of states are studied. The influence of magnetic field, temperature and the form of density of states on concentration dependence of conductivity and magnetization is investigated. The correlated hopping is shown to cause the electron-hole asymmetry of transport and ferromagnetic properties of narrow band materials.

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“…3) becomes somewhat smeared even in the absence of spin dynamics, but the smearing is not so strong as in the FM case [10]. In this self-consistent approximation, the analytical properties are violated for both I > 0 and I < 0 (Table 1).…”

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confidence: 94%

“…[5]) and is a quantum effect that is small in 1/S. Unlike the FM case, where the singularity has one-sided form and non-quasiparticle (incoherent) contributions to the density of state plays main role [10], the logarithmic contribution is symmetric with respect to the Fermi level. Note that after formal expansion in 1/z the contributions to the Green's function with the Fermi functions are canceled in the paramagnetic phase to first order [12].…”

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confidence: 99%

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The Kondo effect in periodic narrow-band systems

Irkhin

Zarubin

2000

Eur. Phys. J. B

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The Kondo divergences owing to interaction of current carriers with local moments in highly correlated electron systems are considered within the Hubbard and s-d exchange models with infinitely strong onsite interaction, the many-electron Hubbard representation being used. The picture of density of states containing a peak at the Fermi level is obtained. Various forms of the self-consistent approximation are used. The problem of the violation of analytical properties of the Green's function is discussed. Smearing of the "Kondo" peak owing to spin dynamics and finite temperatures is investigated.PACS The problem of strong correlations and magnetism in many-electron systems is one of the most important in the solid state theory. Since the Hubbard's works of 60's, a great progress has been achieved in understanding electronic structure of systems with strong on-site interaction. Last time, the role of the Kondo effect has been discussed within the large-d approach (d is space dimensionality) which reduces the initial periodic Hubbard model to an effective Anderson impurity model [1,2]. Besides the Hubbard bands, an important role in the formation of density of states (DOS) picture belongs to a peak at the Fermi level, which was found for both half-filled and doped case (the latter case is considered in [2,3]). It should be noted that this approach meets with a number of computational difficulties (e.g., consideration of finite temperatures is needed, and the low-temperature limit is non-trivial). The structure of the spectrum in large-d approaches is confirmed by the Monte-Carlo calculations. On the other hand, this feature was not reproduced by most preceding analytical approaches. In particular, the Hubbard-III approximation [4] does not take into account contributions of Fermi-like excitations in a proper way because of its single-site character. A detailed analysis of this approximation was performed in Refs. [5,6] within the large-z (z is nearest-neighbor number) expansion.In the present paper we present a treatment that is based on the method of equations of motion for the many-electron Hubbard operators [7,8] and is much more simple than the large-d approach. As the zero order this approach reduces to the simplest Hubbard-I approximation. General expressions for 1/zcorrections were obtained in Ref. [5]. Unfortunately, the terms with the one-particle occupation numbers (which just describe the Kondo effect) were neglected in Refs. [5,6], and only a classical approximation was considered in Ref. [6].We start from the s-d exchange model with the large s-d coupling parameter |I|,where t k is the band energy, H d is the Heisenberg Hamiltonian of the localized-spin system, σ are the Pauli matrices. In the limit |I| → α∞ (here and hereafter α = sign I = ±), it is convenient to pass to the atomic representation of the Hubbard operators X βγ i = |iβ iγ| where H sd (the second term in (1)) takes the diagonal form [9]. For the electron concentration n < 1, after performing the procedure of projection onto the c...

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Electron spectrum and stability of the saturated ferromagnetic state in a Hubbard model with strong correlations

Cited by 12 publications

References 28 publications

Electron correlations in narrow energy bands: modified polar model approach

Electron correlations in narrow energy bands: modified polar model approach

Mott Transition, Ferromagnetism and Conductivity in the Generalized Hubbard Model

The Kondo effect in periodic narrow-band systems

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