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1
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One-Dimensional Falicov-Kimball Model in the Strong Coupling Limit

100%
Farkašovský P., Bat'ko I.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
307-310
EN
We studied the ground state properties of the one-dimensional Falicov-Kimball model in the strong coupling limit for special periodic and aperiodic configurations of ions. The ground state phase diagrams of the model for nearest neighbor and next nearest neighbor hopping are discussed.
2
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Phase Transitions in a Coupled Electron and Spin Model on the Shastry-Sutherland Lattice

100%
Farkašovský P., Čenčariková H.
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EN
The thermodynamics of a simple electron-spin model proposed recently for a description of magnetization processes in rare-earth tetraborides is studied numerically by the canonical Monte Carlo method in two-dimensions. The model is based on the coexistence of two subsystems, and namely, the spin subsystem described by the Ising model and the electronic subsystem described by the free-electron model on the Shastry-Sutherland lattice (SSL). Moreover, both subsystems are coupled by the anisotropic spin-dependent interaction of the Ising type. At T=0 the system exhibits the magnetization plateau (MP) at m/m_s=1/2, 1/3, 1/5, 1/7, 1/9 and 1/11 of the saturated spin magnetization m_s. For the largest phases corresponding to m/m_s=0, 1/3 and 1/2 we have examined the nature of the phase transitions from the low-temperature ordered phase (LTOP) to the high-temperature disordered phase (HTDP). It is shown that all phases persist also at finite temperatures (up to the critical temperature T_c) and that the phase transition at the critical point is of the second order for the m/m_s=0 phase and of the first order for the m/m_s=1/3 and 1/2 phases.
3
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First-Principles Study of Kondo Insulator SmB_{6}

81%
Gmitra M., Čenčariková H., Farkašovský P.
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vol. 126
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issue 1
298-299
EN
We applied the Perdew-Burke-Ernzerhof hybrid functional (PBE0) within the density functional theory (DFT) to study electronic properties of the heavy fermion Kondo semiconductor SmB_{6}. The calculation of the Hartee-Fock exchange contribution to the exact-exchange within the atomic sphere approximation for bulk SmB_{6} represents a computationally efficient, parameter-free method that provides good qualitative and quantitative agreement with photoemission experiments. Specifically, we found an energy difference of 7 eV between the occupied and unoccupied correlated Sm f states. Furthermore, the spin-orbit coupling yields a splitting of the occupied Sm f states of about 1 eV in agreement with recent angular resolved photoemission spectroscopy. The electronic spectrum in the vicinity of the X point shows a hybridization between the Sm 5d conduction band and the localized Sm 4f states at the Fermi level. This might lead to a transport gap opening.
4
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Thermodynamics of the Generalized Spin-One-Half Falicov-Kimball Model in Two Dimensions

81%
Žonda M., Farkašovský P., Čenčariková H.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
104-106
EN
The extrapolation of small-cluster exact-diagonalization calculations and the Monte Carlo method is used to study the spin-one-half Falicov-Kimball model extended by the spin-dependent Coulomb interaction (J) between the localized f and itinerant d electrons as well as the on-site Coulomb interaction (U_{ff}) between the localized f electrons. It is shown that in the symmetric case the ground-state phase diagram of the model has an extremely simple structure that consists of only two phases, and namely, the charge-density-wave phase and the spin-density-wave phase. The nonzero temperature studies showed that these phases persist also at finite temperatures. The same calculations that we performed for unsymmetric case showed that charge and spin ordering can be destroyed simultaneously or consecutively.
5
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Ground States of the Spin-One-Half Falicov-Kimball Model with Hund's Rule Coupling in Two Dimensions

81%
Čenčariková H., Farkašovský P., Tomašovičová N., Žonda M.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
101-103
EN
The spin-one-half Falicov-Kimball model with spin-dependent on-site interaction between localized (f) and itinerant (d) electrons is studied by small-cluster exact-diagonalization calculations and a well-controlled approximative method in two dimensions. The results obtained are used to categorize the ground-state configurations according to common features (charge and spin ordering) for all f and d electron concentrations (n_f and n_d) on finite square lattices. It is shown that only a few configuration types form the basic structure of the charge phase diagram in the n_f-n_d plane. In particular, the largest regions of stability correspond to the phase segregated configurations and configurations that can be considered as mixtures of chessboard configurations and the full (empty) lattice. Since the magnetic phase diagram is much richer than the charge phase diagram, the magnetic superstructures are examined only at selected values of f and d electron concentrations.
6
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Ground States of the Falicov-Kimball Model Extended by Nonlocal Coulomb Interactions

81%
Čenčariková H., Farkašovský P., Žonda M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
287-290
EN
The small-cluster exact-diagonalizations are used to study the ground states of the Falicov-Kimball model extended by nonlocal Coulomb interactions (the nearest-neighbour interaction U_{nn} and the correlated hopping t'). It is shown that the ground-state phase diagrams found for the conventional Falicov-Kimball model are strongly changed when the nonlocal interactions are added. This is illustrated for two selected values of the on-site Coulomb interaction (U) that represent typical behaviours of the model in the intermediate and strong coupling limit. A number of remarkable results are found. (i) The phase separation takes place for a wide range of U_{nn} and t' in both interaction limits. (ii) New types of inhomogeneous charge ordering are observed for nonzero U_{nn} and t'. (iii) Depending on the values of U_{nn} and t', the model is able to describe both the continuous as well as discontinuous changes of the f-electron occupation number.
7
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The Influence of Lattice Defects on the Ground-State Properties of the Falicov-Kimball Model in Two Dimensions

81%
Žonda M., Farkašovský P., Čenčariková H.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
291-294
EN
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.
8
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Ground-State Phase Diagram of the Extended Ising Model on the Shastry-Sutherland Lattice

81%
Čenčariková H., Farkašovský P., Puchala P.
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vol. 126
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issue 1
46-47
EN
The ground-state phase diagram of the Ising model on the Shastry-Sutherland lattice with the first (J_1), second (J_2), third (J_3) and fourth (J_4) nearest neighbour spin couplings is studied using the exact and well controlled numerical method. It is shown that switching on of the J_3 and J_4 interactions (in addition to usually considered J_1 and J_2 interactions) leads to stabilization of the following dominant magnetic phases with m/m_s=1/9, 1/6, 4/9, 1/2 and 5/9, which is manifested in appearance of new magnetization plateaus on the magnetization curve of the model at given values of m/m_s. The obtained results are consistent with experimental measurements of magnetization curves in selected rare-earth tetraborides.
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