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    Wyświetlanie 1-15 z 15
    Tytuł:
    Application of Statistical Spin Liquid Concept to High-Temperature Superconductivity
    Autorzy:
    Byczuk, K.
    Spałek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1930571.pdf
    Data publikacji:
    1994-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.27.+a
    74.20.Mn
    Opis:
    We apply the concept of statistical spin liquid, in which the doubly occupied quasimomentum configurations {|k⇅⟩} for quasiparticles are excluded from the Fock space, to a planar superconductor with real space pairing. The results compare very well with experimental data for the cuprates, namely (i) the condensed state appears only for the number of holes 0 < δ < 0.15-0.25; (ii) the temperature dependence of the gap is close to the BCS result, but the gap has systematically lower value and is of an extended s-wave form.
    Źródło:
    Acta Physica Polonica A; 1994, 85, 2; 337-340
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Kondo-Lattice Metallic and Semiconducting States and Their Instabilities
    Autorzy:
    Spałek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2011221.pdf
    Data publikacji:
    2000-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.27.+a
    71.10.-w
    71.10.Fd
    Opis:
    We review briefly recent results concerning the stability of para-, ferro-, and antiferromagnetic states in the Kondo-lattice limit. Both the macroscopic quantities such as the specific heat and the electrical resistivity, as well as the magnitude of the magnetic moment and the mass enhancement (together with its spin dependence) are discussed.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 1; 71-79
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    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:
    Unconventional Superconducting States of an Almost Localized Fermionic Liquid with Nonstandard Quasiparticles: Generalized Gutzwiller Approach
    Autorzy:
    Kaczmarczyk, J.
    Jędrak, J.
    Spałek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1536614.pdf
    Data publikacji:
    2010-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.27.+a
    71.10.Ca
    Opis:
    We apply the concept of generalized (almost localized) Fermi liquid and associated with it unconventional superconductivity with Cooper pairs composed of quasiparticles with the spin dependent masses (in an applied field) and with the effective field, both induced by electron correlations. The pairing among quasiparticles takes place either in reciprocal space (Sect. 2) or in real space (Sect. 3) and is induced by the kinetic exchange of either superexchange (in the generic narrow-band situation) or Kondo-type interaction (in the Kondo-lattice limit of the periodic Anderson model). While the main features of this type of Fermi liquid have been introduced earlier, we present here a picture which is applicable to both heavy-fermion and high-$T_{c}$ superconductivity within a single narrow-band representation of correlated states. Our approach introduces a set of additional concepts (spin-dependent masses, effective fields induced by electron correlations), for which the Landau concept of the Fermi liquid represents still a workable scheme. In the limit of the Kondo lattice, we present the phase diagram incorporating the Fulde-Ferrell-Larkin-Ovchinnikov phase within the BCS-type of pairing, whereas in that of the t-J model we show that the proper choice of renormalization factors and constraints is crucial for the mean-field description of the superconducting state.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 2; 261-266
    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:
    Theory of Unconventional Superconductivity in Strongly Correlated Systems: Real Space Pairing and Statistically Consistent Mean-Field Theory - in Perspective
    Autorzy:
    Spałek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1431227.pdf
    Data publikacji:
    2012-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.27.+a
    74.70.Tx
    74.20.-z
    Opis:
    In this brief overview we discuss the principal features of real space pairing as expressed via corresponding low-energy (t-J or periodic Anderson-Kondo) effective Hamiltonian, as well as consider concrete properties of those unconventional superconductors. We also rise the basic question of statistical consistency within the so-called renormalized mean-field theory. In particular, we provide the phase diagrams encompassing the stable magnetic and superconducting states. We interpret real space pairing as correlated motion of fermion pair coupled by short-range exchange interaction of magnitude J comparable to the particle renormalized band energy ≈ tx, where x is the carrier number per site. We also discuss briefly the difference between the real-space and the paramagnon-mediated sources of superconductivity. The paper concentrates both on recent novel results obtained in our research group, as well as puts the theoretical concepts in a conceptual as well as historical perspective. No slave-bosons are required to formulate the present approach.
    Źródło:
    Acta Physica Polonica A; 2012, 121, 4; 764-784
    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:
    Kondo-Lattice Metals and Semiconductors with Compensated Magnetic Moments: a Brief Overview
    Autorzy:
    Spałek, J.
    Doradziński, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2011147.pdf
    Data publikacji:
    1999-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.27.+a
    71.10.Fd
    75.30.Mb
    Opis:
    We provide a brief overview of recent theoretical results concerning the metallic and insulating states with very heavy quasiparticle masses and almost compensated magnetic moments, primarily in the antiferromagnetic state. The temperature dependence of the Kondo-insulator band gap is also discussed.
    Źródło:
    Acta Physica Polonica A; 1999, 96, 5; 677-688
    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:
    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:
    Anderson-Kondo Lattice Hamiltonian from the Anderson-Lattice Model: A Modified Schrieffer-Wolff Transformation and the Effective Exchange Interactions
    Autorzy:
    Kądzielawa-Major, E.
    Spałek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1374041.pdf
    Data publikacji:
    2014-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.20.Eh
    71.27.+a
    71.70.Gm
    Opis:
    We derive the Anderson-Kondo lattice model by applying canonical perturbation expansion for the Anderson-lattice model in direct space. The transformation is carried out up to the fourth order by a modified Schrieffer-Wolff transformation: we separate the part of hybridization term responsible for the high-energy processes (involving the largest in-the-system intraatomic Coulomb interaction between f electrons) and replace it with the virtual processes in higher orders. The higher-order processes lead to three separate exchange interactions. The obtained Hamiltonian contains both the Kondo (f-c) and the superexchange (f-f) interactions, as well as a residual hybridization responsible for the heavy-quasiparticle formation. This effective Hamiltonian can be used to analyze the magnetic or the paired states, as well their coexistence in heavy-fermion systems. The magnitudes of both the Kondo exchange and the superexchange integrals are estimated as a function of bare hybridization magnitude.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 4a; A-100-A-103
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-15 z 15

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