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Wyświetlanie 1-15 z 102
Tytuł:
Gaussian Fluctuations of Two Molecular Fields in the Blume-Emery-Griffiths Model
Autorzy:
Jaworski, W.
Jacyna-Onyszkiewicz, Z.
Powiązania:
https://bibliotekanauki.pl/articles/1505093.pdf
Data publikacji:
2011-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Dg
75.10.Hk
75.10.Jm
Opis:
The Blume-Emery-Griffiths model for spins S=1 in a bilayer with z=5 nearest neighbours is studied with the use of Gaussian fluctuations approximation. The fluctuations of two molecular fields, connected with two order parameters, are introduced. Their influence on phase diagrams for non-negative values of the biquadratic coupling constant is taken under consideration. The results are compared with those obtained by the mean-field approximation and discussed.
Źródło:
Acta Physica Polonica A; 2011, 119, 6; 846-849
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin Chain in Magnetic Field: Limitations of the Large-N Mean-Field Theory
Autorzy:
Wohlfeld, K.
Chen, Cheng-Chien
van Veenendaal, M.
Devereaux, T.
Powiązania:
https://bibliotekanauki.pl/articles/1384813.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
75.10.Jm
75.10.Pq
Opis:
Motivated by the recent success in describing the spin and orbital spectrum of a spin-orbital chain using a large-N mean-field approximation, we apply the same formalism to the case of a spin chain in the external magnetic field. It occurs that in this case, which corresponds to N=2 in the approximation, the large-N mean-field theory cannot qualitatively reproduce the spin excitation spectra at high magnetic fields, which polarize more than 50% of the spins in the magnetic ground state. This, rather counterintuitively, shows that the physics of a spin chain can under some circumstances be regarded as more complex than the physics of a spin-orbital chain.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 201-203
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Heisenberg Model of a Ferromagnetic Monolayer Deposited on a Non-Magnetic Bulk Substrate
Autorzy:
Jaworski, W.
Powiązania:
https://bibliotekanauki.pl/articles/1810418.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Dg
75.10.Hk
75.10.Jm
Opis:
A model describing a Heisenberg ferromagnetic monolayer (in a magnetic field) interacting with its non-magnetic bulk substrate is formulated. We use reduced-density operators to show that physical properties of the monolayer are affected by its interaction with the environment. Particularly the influence of the substrate lattice vibrations on the monolayer exchange parameter is examined. The Gaussian-type orbitals were used to calculate the distance dependence of the exchange parameter and the many-body Green functions to calculate the temperature dependence of the magnetization. Finally, the influence of the Debye temperature of the substrate on the magnetization of the monolayer is depicted. Although the resultant effect is not prominent, we state that interaction of ultrathin magnetic films with their environment has to be taken into account in the construction of the reduced-density operator.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 171-173
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin-1/2 XXZ Diamond Chain within the Jordan-Wigner Fermionization Approach
Autorzy:
Verkholyak, T.
Strečka, J.
Jaščur, M.
Richter, J.
Powiązania:
https://bibliotekanauki.pl/articles/1535012.pdf
Data publikacji:
2010-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.10.Pq
Opis:
The spin-1/2 XXZ diamond chain is considered within the Jordan-Wigner fermionization. The fermionized Hamiltonian contains the interacting terms which are treated within the Hartree-Fock approximation. We obtain the ground-state magnetization curve of the model for some particular cases and compare the results with the exact diagonalization data for finite chains of 30 spins and known exact results. We also analyze the validity of the suggested approximation.
Źródło:
Acta Physica Polonica A; 2010, 118, 5; 978-979
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Antiferromagnetic Order in the Hubbard Model: Spin-Charge Rotating Reference Frame Approach
Autorzy:
Zaleski, T.
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1812334.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
75.10.Jm
Opis:
We study the antiferromagnetic phase of three-dimensional Hubbard model with nearest neighbors hopping on a bipartite cubic lattice. We use the quantum SU(2)×U(1) rotor approach that yields a fully self-consistent treatment of the antiferromagnetic state that respects the symmetry properties of the model and satisfies the Mermin-Wagner theorem. As our theory describes the evolution from a Slater (U ≪ t) to a Mott-Heisenberg (U ≫ t) antiferromagnet, we present the phase diagram of the antiferromagnetic Hubbard model as a function of the crossover parameter U/t.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 247-251
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Frustrated Magnetism in Vanadium Oxides
Autorzy:
Thalmeier, P.
Schmidt, B.
Yushankhai, V.
Takimoto, T.
Powiązania:
https://bibliotekanauki.pl/articles/1810285.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.10.Lp
Opis:
The effect of frustration in various localized and itinerant vanadium oxide compounds is discussed within next nearest neighbors Heisenberg and spin fluctuation models, respectively. In the localized moment case the S=1/2 $J_1-J_2$-model on a square lattice exhibits a rich phase diagram with magnetic as well as exotic hidden order phases due to the interplay of frustration and quantum fluctuations. Their signatures in the high field magnetization and in magnetocaloric quantities are surveyed. The possible quantum phase transitions are discussed and applied to layered vanadium oxides of the type $AA'VO(PO_4)_2$ where A, A' = Pb, Zn, Sr, Ba, Cd. In itinerant electron systems magnetic frustration may emerge as a result of electron correlations on a geometrically frustrated lattice. This mechanism causes enhanced spin fluctuations in a large region of momentum space and therefore can lead to a heavy fermion state at low temperatures as in the 3d spinel compound $LiV_2O_4$. The evidence from neutron scattering and NMR experiments is discussed within self-consistent renormalization theory based on local density approximation band structure calculations.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 53-58
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ground-state spin of Hubbard ladder model with infinite electron repulsion
Autorzy:
Cheranovskii, V.
Ezerskaya, E.
Klein, D.
Tokarev, V.
Powiązania:
https://bibliotekanauki.pl/articles/1054813.pdf
Data publikacji:
2017-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
75.10.Jm
Opis:
We apply perturbation theory and cyclic spin permutation formalism to study the lowest energy states of the infinite-repulsion Hubbard model on n-leg ladders with alternating values of one-site energies α_{i} for neighboring rungs. We establish the "ferromagnetic" character of ladder ground-state at electron densities in the interval 1 - (2n)¯¹ ≤ ρ ≤ 1 and sufficiently large alternation of one-site energies of neighbor rungs of the ladder. We also show the stability of this state against the small deviations of the values of α_{i} in contrast to the case of two-leg ladder formed by weakly interacting neighbor rungs with equal one-site energies.
Źródło:
Acta Physica Polonica A; 2017, 131, 4; 916-918
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of Contractor Renormalization Group to the Heisenberg Zig-Zag and the Hubbard Chain
Autorzy:
Cichy, K.
Tomczak, P.
Powiązania:
https://bibliotekanauki.pl/articles/2047340.pdf
Data publikacji:
2007-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.10.Cc
03.65.Fd
75.10.Jm
71.10.Fd
Opis:
The contractor renormalization group method was devised in 1994 by Morningstar and Weinstein. It was primarily aimed at extracting the physics of lattice quantum field theories (like lattice quantum chromodynamics). However, it is a general method of analyzing Hamiltonian lattice systems, e.g. Ising, Heisenberg or Hubbard models. The aim of this work is to show the application of contractor renormalization group method to one-dimensional quantum systems - the Heisenberg zig-zag model and the Hubbard chain. As a test of the method, the ground state energy of these systems will be calculated.
Źródło:
Acta Physica Polonica A; 2007, 111, 5; 773-780
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Pentagonal Ring - Galois Extensions and Crystallography
Autorzy:
Labuz, M.
Lulek, T.
Powiązania:
https://bibliotekanauki.pl/articles/1033704.pdf
Data publikacji:
2017-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
03.65.Fd
03.67.Lx
02.10.Ud
02.10.De
Opis:
The Galois symmetry of exact Bethe Ansatz eigenstates for magnetic pentagonal ring is shown to bear a close analogy to some crystallographic constructions. Automorphisms of number field extensions associated with these eigenstates prove to be related to choices of the Bravais cells in the finite crystal lattice ℤ₂×ℤ₂, responsible for extension of the cyclotomic field by the Bethe parameters.
Źródło:
Acta Physica Polonica A; 2017, 132, 1; 97-99
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Strongly Anisotropic S=1 (Pseudo) Spin Systems: from Mean Field to Quantum Monte-Carlo
Autorzy:
Panov, Yu.
Moskvin, A.
Konev, V.
Vasinovich, E.
Ulitko, V.
Powiązania:
https://bibliotekanauki.pl/articles/1030506.pdf
Data publikacji:
2018-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Hk
75.10.Jm
74.25.Dw
Opis:
The S=1 pseudospin formalism was recently proposed to describe the charge degree of freedom in a model high-T_{c} cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu^{1+;2+;3+}. With small corrections the model becomes equivalent to a strongly anisotropic S=1 quantum magnet in an external magnetic field. We have applied a generalized mean-field approach and quantum Monte-Carlo technique for the model 2D S=1 system to find the ground state phase with its evolution under deviation from half-filling and different correlation functions. Special attention is given to the role played by the on-site correlation ("single-ion anisotropy").
Źródło:
Acta Physica Polonica A; 2018, 133, 3; 426-428
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Kinetically-Driven Frustration in Hybrid Spin Ladders
Autorzy:
Carvalho, R.
Pereira, M.
Lyra, M.
Rojas, O.
Strecka, J
Powiązania:
https://bibliotekanauki.pl/articles/1199484.pdf
Data publikacji:
2014-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.10.Pq
05.70.Ce
Opis:
We introduce a spin ladder model incorporating localized and delocalized spins, which is exactly solvable using the decoration-iteration and transfer-matrix techniques. Quantum correlations between delocalized spins induce an antiferromagnetic coupling between the spin chains that competes with a direct ferromagnetic exchange coupling. A resulting kinetically-driven frustration is predominant in the regime of low temperatures and large hopping amplitudes. We provide the full ground-state phase diagram, as well as the frustration diagram on distinct coupling regimes.
Źródło:
Acta Physica Polonica A; 2014, 126, 1; 12-13
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ising Ferromagnetism of Composite Fermions
Autorzy:
Výborný, K.
Čertík, O.
Pfannkuche, D.
Wodziński, D.
Wójs, A.
Quinn, J. J.
Powiązania:
https://bibliotekanauki.pl/articles/2047042.pdf
Data publikacji:
2006-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
73.43.-f
71.10.Pm
75.10.Jm
Opis:
The quantum Hall ferromagnets at the half-filling of a pair of degenerate electron or composite fermion Landau levels are studied by exact numerical diagonalization. The results obtained using open and closed geometries (rectangular - with periodic boundary conditions and spherical) are compared. The ferro- and paramagnetic ground states are identified in finite-size energy spectra, and the pair-correlation functions are used in search of the domain structure at half-polarization.
Źródło:
Acta Physica Polonica A; 2006, 110, 3; 409-415
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ground-State Phase Diagram of Geometrically Frustrated Ising-Heisenberg Model on Doubly Decorated Planar Lattices
Autorzy:
Čanová, L.
Strečka, J.
Dely, J.
Jaščur, M.
Powiązania:
https://bibliotekanauki.pl/articles/1813794.pdf
Data publikacji:
2008-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.50.+q
75.10.Hk
75.10.Jm
Opis:
Ground-state phase diagram of the mixed spin-1/2 and spin-1 Ising-Heisenberg model on doubly decorated planar lattices is examined using the generalized decoration-iteration transformation. The main attention is devoted to the comparison of the ground-state properties of the quantum Ising-Heisenberg model and its semi-classical Ising analogue.
Źródło:
Acta Physica Polonica A; 2008, 113, 1; 449-452
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Some New Approaches of the XXX Heisenberg Model of the Two-Magnon Sector
Autorzy:
Łabuz, M.
Milewski, J.
Lulek, T.
Powiązania:
https://bibliotekanauki.pl/articles/1030760.pdf
Data publikacji:
2018-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
03.65.Fd
03.67.Lx
02.10.Ud
02.10.De
Opis:
XXX Heisenberg s-1/2 model has been examined in detail during last decades, however, recently one may find some new insights into that issue. Among several approaches describing the eigenproblem for the finite case, a close look into the structure of Bethe equations (BE) for the two-magnon sector case seems to be particularly interesting. BE enable us to evaluate parameters labeling eigenstates of a magnet, however to find appropriate sets of winding numbers, which parametrize BE, one has to apply the Inverse Bethe Ansatz method. On the other hand, one may choose a different - combinatoric approach - which also parametrizes Bethe eigenstates, with the use of rigging numbers describing string configurations. We present an idea of comparison of the concepts mentioned above for the particular case of two-spin deviations sector.
Źródło:
Acta Physica Polonica A; 2018, 133, 3; 444-446
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Point Group Interpretation of Galois Symmetry of Bethe Ansatz Solutions of Magnetic Pentagonal Ring
Autorzy:
Lulek, B.
Lulek, T.
Łabuz, M.
Milewski, J.
Powiązania:
https://bibliotekanauki.pl/articles/1385546.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
03.65.Fd
03.67.Lx
02.10.Ud
02.10.De
Opis:
Exact solutions of the eigenproblem of the magnetic pentagonal ring exhibit the arithmetic symmetry expressed in terms of a Galois group of a finite extension of the prime field Q of rationals. We propose here a geometric interpretation of this symmetry in the interior of the Brillouin zone, in terms of point groups. Explicitly, it is a subgroup of the direct product C₄ × D₄. We present also the appropriate irreducible representations of the group.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 336-338
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 102

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