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Tytuł:
Partial Localization of Correlated Electrons in an Orbitally Degenerate Narrow Band: Spin Dependent Masses, Saturated Ferromagnetism, and the Effective s-d Model
Autorzy:
Jędrak, J.
Spałek, J.
Zwicknagl, G.
Powiązania:
https://bibliotekanauki.pl/articles/2047325.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
75.10.Lp
Opis:
We determined the localization threshold in a partially filled and doubly degenerate model of correlated electrons. Particular emphasis is put on a non-integer band filling n≥1, when the system decomposes into the localized and the itinerant subsystems; this situation is described by an effective s-d model. A simultaneous transition to the ferromagnetic state is discussed as driven by the Hund rule coupling combined with the effective field coming from the correlations. The dependence of the quasiparticle mass on the spin direction appears naturally in the spin-polarized phase and is attributed to the electron correlation effects, as is also a metamagnetic transition in an applied field. Although the main results were obtained within the saddle point slave-boson approach, their qualitative features are discussed in general terms, i.e. as a transition from quantum-mechanical indistinguishability of particles forming the Fermi fluid to a two-component situation.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 619-633
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Comparative Study of the Electronic Structures of $Fe_3O_4$ and $Fe_2SiO_4$
Autorzy:
Piekarz, P.
Oleś, A.
Parlinski, K.
Powiązania:
https://bibliotekanauki.pl/articles/1536886.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
71.38.-k
Opis:
The electronic properties of two spinels $Fe_3O_4$ and $Fe_2SiO_4$ are studied by the density functional theory. The local Coulomb repulsion U and the Hund exchange J between the 3d electrons on iron are included. For U = 0, both spinels are half-metals, with the minority $t_{2g}$ states at the Fermi level. Magnetite remains a metal in a cubic phase even at large values of U. The metal-insulator transition is induced by the $X_3$ phonon, which lowers the total energy and stabilizes the charge-orbital ordering. $Fe_2SiO_4$ transforms to a Mott insulating state for U > 2 eV with a gap $Δ_g$ ~ U. The antiferromagnetic interactions induce the tetragonal distortion, which releases the geometrical frustration and stabilizes the long-range order. The differences of electronic structures in the high-symmetry cubic phases and the distorted low-symmetry phases of both spinels are discussed.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 307-312
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Non-Fermi Liquid Behavior of Correlated Fermions in Applied Field
Autorzy:
Korbel, P.
Spałek, J.
Wójcik, W.
Powiązania:
https://bibliotekanauki.pl/articles/1964622.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
71.10.Fd
Opis:
We have determined an instability of the Fermi-liquid state of almost localized fermions in an applied magnetic field. It is proposed that a transition to a strongly correlated fermions (statistical-spin-liquid) state takes place at that point. The resultant magnetization curve and the field dependence of the specific heat are calculated and compared with those for CeRu$\text{}_{2}$Si$\text{}_{2}$.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 323-326
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Stabilization of Kondo Semiconductor State by Sb Doping of $CeNi_{1-δ}Sn_{1+δ}$ and the General Criterion of Its Appearance
Autorzy:
Spałek, J.
Ślebarski, A.
Powiązania:
https://bibliotekanauki.pl/articles/1812262.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
72.15.Qm
71.30.+h
Opis:
Semimetallic off-stoichiometric $CeNi_{1-δ}Sn_{1+δ-x}Sb_x$ system with δ≈0.06 is shown to transform into a Kondo semiconductor upon the substitution of few percent of Sb for Sn. The full-gap formation is associated with f-electron localization induced by the combined effect of the collective Kondo-singlet formation and the atomic disorder. Namely, the extra valence electrons introduced with the Sb doping (one per Sb atom) contribute additionally to the formation of the collective Kondo spin-singlet state at low temperatures, as seen by a substantial reduction of the magnetic susceptibility. The precise general definition of the Kondo semiconductor is provided and the difference with either the simple band or the Mott-Hubbard insulators is stressed.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 7-14
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin Polarons in Weakly Doped Antiferromagnets: Experimental Evidence Obtained for Cuprates
Autorzy:
Wróbel, P.
Suleja, W.
Eder, R.
Powiązania:
https://bibliotekanauki.pl/articles/1812270.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.10.Fd
74.72.-h
Opis:
The mechanism of spin polaron formation in moderately doped cuprates is discussed. These objects represent holes embedded into heavy clouds formed by spin fluctuations. Wave functions of spin polarons are spatially confined due to the increase in the exchange energy which is induced by hole motion giving rise to the creation of spin fluctuations. These wave functions are eigenstates of an "unperturbed" Hamiltonian which is defined by processes responsible for the tendency toward confinement. The eigenstates transform according to different irreducible representations of the point group reflecting the symmetry of the problem. Thus, the spin polarons being local wave functions resemble orbital states. The spectrum of optical conductivity in the mid-infrared range is determined by transitions between s-wave and p-wave spin polarons. The hybridization between different spin polarons which is induced by some high order processes gives rise to the formation of energy bands. The pronounced transfer of the spectral weight between different bands is induced by the coupling between spin fluctuations created by the hopping hole and local quantum fluctuations in the empty antiferromagnetic background from which an electron has been rejected, for example during the photoemission process. The form of the energy dispersion for spin polarons gives rise to the formation of a small Fermi surface at the low hole-doping range. These three above mentioned phenomena were observed in cuprates which seems to confirm the spin polaron scenario. The discussion of related experiments is the additional objective of this paper.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 51-58
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Correlated Electron Systems of Different Dimensionalities
Autorzy:
Kurzyk, J.
Wójcik, W.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1812297.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
71.10.Fd
Opis:
The optimized single-particle wave functions contained in the parameters of the Hubbard model (hopping integral t and intraatomic interaction U) are determined explicitly in the correlated state for electronic systems of various symmetries and dimensions: Hubbard chain, square and triangular lattices, and the three cubic lattices: SC, BCC, and FCC. In effect, the electronic properties of these structures as a function of the interatomic distance R are obtained. In most cases, the model parameters do not scale linearly with the lattice constant. Also, the atomic part of the total ground state energy changes with the U/t ratio and therefore should be (and is) included in the analysis. The solutions of dimensions D>1 are analyzed by utilizing the approximate Gutzwiller treatment.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 175-178
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Optimized Wannier Functions for Hubbard Chain
Autorzy:
Kurzyk, J.
Wójcik, W.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1810395.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
71.10.Fd
Opis:
One-dimensional atomic chain with a variable-range hopping is described within the extended Hubbard model. The Gutzwiller-ansatz approximation is used to determine the optimized single-particle (Wannier) wave functions in the correlated state. Hopping integral up to the third neighbors is taken into account and the results are compared with those for the infinite hopping range. Ground state energy of the system is compared with that making use of the rigorous Lieb-Wu solution with the optimized wave functions. The evolution of the properties as a function of interatomic distance is discussed.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 114-116
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Superconductivity in Hubbard Model with Correlated Hopping
Autorzy:
Bułka, B. R.
Robaszewska, M.
Powiązania:
https://bibliotekanauki.pl/articles/1955520.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
74.20.Mn
Opis:
Using the slave-boson method in its spin- and charge-rotational invariant representation we determine stability of the superconducting state in the Hubbard model with correlated hopping. In general the term with correlated hopping violates electron-hole symmetry, however, in the special case when the correlated hopping integral X is equal to the uncorrelated hopping integral t the electron-hole symmetry remains. We investigate this case and show that correlations induced by onsite Coulomb interactions U yield to the normal state with exactly single occupied sites (corresponding to |U=∞⟩). The phase diagram of the superconducting state is determined for the different electron concentration n. At the half-filled band (n=1) a direct transition from the Mott insulator to the superconducting state occurs.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 363-366
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Correlated Fermions Close to Mott Localization: Deviations from Landau Fermi-Liquid Picture
Autorzy:
Spałek, J.
Wójcik, W.
Korbel, P.
Powiązania:
https://bibliotekanauki.pl/articles/1964564.pdf
Data publikacji:
1997-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
71.10.Fd
Opis:
We summarize the main novel features of almost localized fermions in the presence of au applied magnetic field: (i) the spin dependence of their effective mass, which leads to quantum beats in the de Haas-van Alphen effect and (ii) the presence of a nonlinear molecular field and related metamagnetic behavior.
Źródło:
Acta Physica Polonica A; 1997, 92, 2; 277-280
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
t-J Model Then and Now: a Personal Perspective from the Pioneering Times
Autorzy:
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2047299.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
74.72.-h
71.10.Fd
Opis:
In this overview we sketch briefly the path to the so-called t-J model derived for the first time 30 years ago and provide its original meaning within the theory of strongly correlated magnetic metals with a non-Fermi (non-Landau) liquid ground state. An emergence of the concept of real space pairing is discussed in a historical prospective. A generalization of this model to the many-orbital situation is briefly discussed. The emphasis is put on didactical exposition of ideas, as they were transformed into mathematical language. The concept of hybrid pairing is introduced in the same context at the end.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 409-424
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Kondo Insulating State in CeRhSb$\text{}_{1-x}$Sn$\text{}_{x}$ as a Function of Carrier Number and Its Subsequent Metallization
Autorzy:
Ślebarski, A.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2047307.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
72.15.Qm
71.30.+h
Opis:
A quantum critical point represents an essential singularity in the phase diagram of the electron-correlated compounds. In the CeRhSb$\text{}_{1-x}$Sn$\text{}_{x}$ system we have observed a quantum criticality at the boundary Kondo insulator-non-Fermi liquid state. In this series of compounds, CeRhSb has a Kondo insulating ground state, whereas CeRhSn exhibits a non-Landau Fermi liquid behavior. In view of different types of behavior of CeRhSb and CeRhSn, we review the results of the solution in CeRhSb$\text{}_{1-x}$Sn$\text{}_{x}$ and discuss the effect of a quasi-continuous change of the number of conduction electrons on the gap formation in the Kondo-insulating regime, as well as on the critical behavior appearance near the quantum critical point.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 487-496
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Surprises in Correlated Electron Physics
Autorzy:
Byczuk, K.
Hofstetter, W.
Kollar, M.
Vollhardt, D.
Powiązania:
https://bibliotekanauki.pl/articles/2047313.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
71.27.+a
71.30.+h
Opis:
Strong electronic correlations and especially the interplay between correlations and disorder lead to many interesting and quite unexpected phenomena. A short summary of our recent investigations into the properties of strongly correlated electron systems with and without disorder using the dynamical mean-field theory is presented.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 549-561
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Lieb-Wu Solution, Gutzwiller-Wave-Function, and Gutzwiller-Ansatz Approximations with Adjustable Single-Particle Wave Function for the Hubbard Chain
Autorzy:
Kurzyk, J.
Spałek, J.
Wójcik, W.
Powiązania:
https://bibliotekanauki.pl/articles/2047324.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
71.30.+h
71.10.Fd
Opis:
The optimized single-particle wave functions contained in the parameters of the Hubbard model (t and U) were determined for an infinite atomic chain. In effect, the electronic properties of the chain as a function of interatomic distance R were obtained and compared for the Lieb-Wu exact solution, the Gutzwiller-wave-function approximation, and the Gutzwiller-ansatz case. The ground state energy and other characteristics for the infinite chain were also compared with those obtained earlier for a nanoscopic chain within the exact diagonalization combined with an ab initio adjustment of the single-particle wave functions in the correlated state (exact diagonalization combined with an ab initio method). For the sake of completeness, we briefly characterize also each of the solutions. Our approach completes the Lieb-Wu solution, as it provides the system electronic properties evolution as a function of physically controlable parameter - the interatomic distance.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 603-618
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Stripe Phases in the Hubbard Model
Autorzy:
Góra, D.
Rościszewski, K.
Oleś, A. M.
Powiązania:
https://bibliotekanauki.pl/articles/2012901.pdf
Data publikacji:
2000-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
74.72.-h
75.10.-b
64.60.-i
Opis:
We investigate the magnetic and charge ordering in the stripe phases obtained while using correlated wave functions for finite 8×8 clusters described by the Hubbard model with extended hopping. Nonmagnetic vertical (01) site-centered domain walls and (11) bond-centered stripes are found for the parameters of La$\text{}_{2-x}$Sr$\text{}_{x}$CuO$\text{}_{4}$ and YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+x}$, respectively, at doping δ=1/8. The obtained half-filled domain nonmagnetic walls reproduce the maxima observed in neutron scattering for La$\text{}_{2-x}$Sr$\text{}_{x}$CuO$\text{}_{4}$.
Źródło:
Acta Physica Polonica A; 2000, 97, 1; 225-228
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Influence of Lattice Defects on the Ground-State Properties of the Falicov-Kimball Model in Two Dimensions
Autorzy:
Žonda, M.
Farkašovský, P.
Čenčariková, H.
Powiązania:
https://bibliotekanauki.pl/articles/1813656.pdf
Data publikacji:
2008-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Lp
71.27.+a
71.28.+d
71.30.+h
Opis:
The influence of lattice defects (vacancies) on the ground-state properties of the spinless Falicov-Kimball model is studied by a well-controlled numerical method in two dimensions. It is shown that in the presence of vacancies (distributed randomly) the ground states of the Falicov-Kimball model are phase separated for small f-electron concentrations $n_f$ and exhibit the long-range order for $n_f$ near the half-filled band case $n_f$=1/2. In addition, the dependence of average f-orbital occupancy on the concentration of vacancies is calculated for a wide range of model parameters. The resultant behaviours are used to interpret the experimental data obtained for the mixed-valence system $Sm_{1-x}B_6$.
Źródło:
Acta Physica Polonica A; 2008, 113, 1; 291-294
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł

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