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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:
Strongly Correlated Electrons in a Magnetic Field: Fermi Liquid versus Spin Liquid
Autorzy:
Spałek, J.
Wójcik, W.
Powiązania:
https://bibliotekanauki.pl/articles/1930575.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.28.-d
75.10.Lp
Opis:
We compare the Fermi liquid (FL) and statistical spin liquid (SSL) representations of the electronic properties for strongly correlated systems. In particular, we discuss the entropy, as well as the magnetization as a function of band filling, temperature and magnetic field. These properties are quite different in the two (FL, SSL) states. Antiferromagnetic state disappears for a small number of holes in the doped Mott insulator.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 357-361
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Cooper Pair with Nonzero Momentum in System with Spin Dependent Mass of Quasiparticles
Autorzy:
Kaczmarczyk, J.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2047323.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.24.+q
71.10.Li
Opis:
We consider a single Cooper pair with the spin dependent quasiparticle masses, with and without applied magnetic field. Such situation takes place for the strongly correlated electron systems, where a relatively strong Hubbard interaction differentiates the quasiparticle states in the majority- and the minority-spin subbands. In that situation, the two spin subbands in an applied magnetic field are not only shifted one with respect to the other, but also distorted differently, which results from the electronic correlations. Under these circumstances, the fermionic particles composing the Cooper pair, are quantum mechanically distinguishable. In result, the Cooper pair has a nonzero momentum (i.e. produces a stationary current in a similar manner as electron in the Bloch state), and there exists a critical value of the attractive interaction, below which the bound Cooper-pair state is not formed. The presence of the applied field (included via the Zeeman term) does not alter the picture qualitatively. Importance of these results for the formation of the Fulde-Ferrell-Larkin-Ovchinnikov phase in strongly correlated systems is mentioned.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 595-602
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Correlation Induced Optimization of Wave Functions: the Hubbard Chain
Autorzy:
Spałek, J.
Podsiadły, R.
Wójcik, W.
Powiązania:
https://bibliotekanauki.pl/articles/2013007.pdf
Data publikacji:
2000-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
71.15.Fv
31.25.Nj
Opis:
We determine the explicit form of the single-particle Wannier functions {w$\text{}_{i}(r)}$ appearing in the parameters of quantum models. The method is illustrated on the example of the Hubbard chain, for which we derive the renormalized wave equation starting from a variational principle and by treating the system ground state energy as a functional of {w$\text{}_{i}(r)}$ and their derivatives. In this manner, the optimized basis is obtained only after the electronic correlations have been included in the rigorous Lieb-Wu solution. The results for the ground state energy and the size of the renormalized s-type orbitals, both as a function of interatomic distance, are calculated explicitly.
Źródło:
Acta Physica Polonica A; 2000, 97, 3; 381-384
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:
Coexistence of Spin-Triplet Superconductivity with Antiferromagnetism in Orbitally Degenerate System: Hartree-Fock Approximation
Autorzy:
Zegrodnik, M.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1431255.pdf
Data publikacji:
2012-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.25.Dw
75.10.Lp
Opis:
We consider the coexistence of the Hund's-rule-exchange induced spin-triplet paired state with the antiferromagnetic ordering by starting from the extended Hubbard model for a doubly degenerate band. We use the density of states appropriate for the square lattice and treat the problem in the Hartree-Fock approximation. The temperature dependences of the superconducting gaps, the magnetic moment, and the chemical potential are presented. The free energy in the considered phase is evaluated, as well as the corresponding free energies in four additional phases: paramagnetic, ferromagnetic, superconducting of type A and superconducting of type A1 coexisting with ferromagnetism; they occur in the proper range of parameters: band filling n and the interaction parameters U/W and J/W. The low temperature values of the superconducting gaps and staggered magnetic moment are also analyzed as a function of band filling.
Źródło:
Acta Physica Polonica A; 2012, 121, 4; 801-804
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of Pair Approximation to Bound-Magnetic-Polaron State in Diluted Magnetic Semiconductors
Autorzy:
Bednarski, H.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1403651.pdf
Data publikacji:
2012-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.45.+j
75.30.Et
Opis:
We present a fully quantum-mechanical model of the bound magnetic polaron state in a diluted magnetic semiconductor based on the pair approximation to the exchange interaction among localized magnetic moments (spins). The model is applicable also to the limiting situation of the bound magnetic polaron magnetization due to the spins approaching saturation. On its basis, a simple extension of the Dietl-Spałek bound magnetic polaron theory is proposed and compared with the data for $p-Cd_{0.95}Mn_{0.05}Te$.
Źródło:
Acta Physica Polonica A; 2012, 122, 6; 1052-1055
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Cooper Pair in Two Nonstandard Situations
Autorzy:
Wróbel, P.
Starypan, Z.
Kaczmarczyk, J.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2046740.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.25.Jb
71.10.-w
Opis:
We summarize briefly our recent work on the bound states of two electrons (Cooper pairs) in two nonstandard situations: when the quasiparticle masses depend on spin and when an electron pair is localized on a two-dimensional quantum dot and placed in an applied magnetic field. In both cases we are dealing with an extension of the original Cooper approach. The applicability of the results is briefly mentioned.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 541-548
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:
Spin-Triplet Pairing Induced by Hunds Rule Exchange in Orbitally Degenerate Systems: Hartree-Fock Approximation
Autorzy:
Zegrodnik, M.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1426874.pdf
Data publikacji:
2012-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.25.Dw
75.10.Lp
Opis:
We discuss the spin-triplet pairing mechanism induced by the Hund rule ferromagnetic exchange. We include explicitly the effect of interband hybridization and treat the problem by starting from an extended Hubbard model for a doubly degenerate band, making the simplest Hartree-Fock approximation for the part involving the pairing and the Hubbard interaction. The conditions of stability of various phases are determined as a function of both band filling and microscopic parameters. The phase diagram contains regions of stability of the spin-triplet superconducting phase coexisting with either saturated or non-saturated ferromagnetism. Phase diagrams for the cases of constant density of states and that of square lattice have been provided. The influence of hybridization on the stability of considered phases, as well as the temperature dependences of magnetic moment and the superconducting gap are also discussed.
Źródło:
Acta Physica Polonica A; 2012, 121, 5-6; 1051-1055
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bound-Magnetic-Polaron Molecule in Diluted Magnetic Semiconductors within Heitler-London Approximation
Autorzy:
Bednarski, H.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1492984.pdf
Data publikacji:
2011-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.-b
75.45.+j
75.30.Et
Opis:
We determine the states of a pair of bound magnetic polarons in a diluted magnetic semiconductor by taking into account both the molecular nature of the two-electron wave function in the Heitler-London approximation, as well as the thermodynamic fluctuations of magnetization due to localized 3d spins. We extend the theory of a single bound magnetic polaron to molecular case.
Źródło:
Acta Physica Polonica A; 2011, 120, 5; 967-969
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:
Exchange Interaction as a Source of Real Space Pairing in High Temperature Superconductors and Heavy Fermions: a Brief Overview
Autorzy:
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1860823.pdf
Data publikacji:
1994-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.28.+d
75.10.Lp
74.70.Vy
Opis:
We characterize the principal difference between the pairing induced by the kinetic exchange interactions for the Fermi-liquid and spin-liquid phases. In the case of hybridized electrons the Kondo-exchange induced pairing is invoked, whereas for a single narrow-band case kinetic exchange is responsible for the spin singlet pairing. The former interaction is applied to heavy-fermion systems, whereas the latter is employed to the high temperature superconductors. The current situation concerning the applicability of our theoretical models is briefly and critically assessed.
Źródło:
Acta Physica Polonica A; 1994, 85, 1; 39-52
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
Wyświetlanie 1-15 z 20

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