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  1. 102 Acta Physica Polonica A

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  1. 11 Kamieniarz G.

  2. 11 Oleś A.

  3. 9 Richter J.

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1
Content available remote

Critical and Massive Phases in Spin Chains and Spin Ladders

100%
Sólyom J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
81-90
EN
Spin chains and spin ladders can have a variety of gapless (critical) or gapped (massive) phases depending on the length of the spin and the type of coupling. A brief review of the results on some simple models is given with emphasis on the generation of the Haldane gap in anisotropic spin ladders.
2
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Lieb-Mattis Model for Two Interpenetrating Antiferromagnets

100%
Schmalfuss D., Krüger S., Richter J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
377-380
EN
We investigate a frustrated Lieb-Mattis-like spin-1/2 model that is a reference model for the corresponding square-lattice Heisenberg model describing the unusual magnetic properties of Ba_{2}Cu_{3}O_{4}Cl_{2}. Due to frustration we obtain a rich magnetic phase diagram. We find two critical temperatures in accordance with recent experiments on Ba_{2}Cu_{3}O_{4}Cl_{2}.
3
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Hidden Domain Walls as Elementary Excitations in the Spin-1 Valence-Bond-Solid Model

100%
Fáth G., Sólyom J.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
371-375
EN
Low-energy excitations are studied in the 1D S = 1 antiferromagnetic valence-bond-solid model. The lowest states are found to form a discrete triplet branch, separated from a higher-lying scattering continuum. The elementary excitations are argued to be "hidden" domain walls.
4
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J_{1}-J_{2}-J_{3} Model with Long-Range Lieb-Mattis Interaction

100%
Krüger S. E., Richter J.
Acta Physica Polonica A
|
1997
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vol. 91
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issue 2
377-380
EN
Stimulated by the two-dimensional frustrated Heisenberg antiferromagnet with first-, second-, and third-neighbor couplings (J_{1}-J_{2}-J_{3} model) we consider a corresponding three-parameter model with a long-range antiferromagnetic Lieb-Mattis interaction. This model can be solved exactly and leads to a better understanding of the role of frustration in the J_{1}-J_{2}-J_{3} model. We calculate the correlations in the groundstate and consider their finite size behavior. Furthermore we present the full thermodynamic phase diagram. We find the possibility of a disordered phase at T=0.
5
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On the Energy Spectrum and Ground-State Properties οf the Decorated Heisenberg Spin Tube

100%
Cheranovskii V., Ezerskaya E.
|
EN
The ground-state properties of decorated Heisenberg spin tubes with nearest- and next-nearest-neighbor antiferromagnetic exchange interactions has been studied using perturbation theory and exact diagonalization technique. The possibility of quantum phase transitions mediated by next-nearest neighbor interactions for these tubes is shown.
6
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Real-Space Pair Model Predictions for the NMR Behaviour in High-T_{c} Cuprates

100%
Mukhin S.
Acta Physica Polonica A
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1994
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vol. 85
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issue 1
133-143
EN
A model for real-space singlet pairs, hopping on the quasi 2D antiferromagnetic background of localized spins is further analysed. It is shown that lattice vibrations (if any), which break the symmetry of the in-plane oxygen position with respect to the nearest neighboring copper sites, may strongly influence both the magnitude and the temperature dependence of the ^{17}O NMR relaxation rate. For the Y site a situation is analogous, although the different modes may contribute to the effect. A relation of the results obtained to the Millis-Monien-Pines analysis is discussed. The validity of the mean-field random phase approximation for the description of the 2D antiferromagnet used previously is analysed. It is shown that the 2D fluctuations of the phase of the (bond) mean field parameter lead to the power-law decay with the distance of the corresponding correlation function (which remains finite in the mean field approximation). The spectrum of the phase fluctuations is found to be propagative in the one-loop approximation. An interaction of the real-space singlet pairs with the long-wavelength phase fluctuations is discussed.
7
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Verification of a New Quantum Simulation Approach through Its Application to Heisenberg-Like Models

63%
Liu Z., Ian H.
Acta Physica Polonica A
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2016
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vol. 129
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issue 6
1210-1213
EN
A quantum simulation approach facilitated by the self-consistent algorithm was applied in the present work to ferromagnetic and antiferromagnetic three-dimensional Heisenberg lattices consisting of S = 1 spins. Consequently, the calculated spontaneous magnetizations for the two sorts of lattices are precisely consistent with mean-field theory in the whole temperature range. Especially, the numerical results, such as magnetizations, total energies and total free energies per mole of spins, show no size effects. Thus, the physical properties of a huge bulk magnet can be estimated by performing simulation for a very tiny sample, so that the computational time can be greatly saved.
8
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Zero Temperature Magnetic Frustration in Nona-Membered s=3/2 Spin Rings with Bond Defect

63%
Antkowiak M., Kozłowski P., Kamieniarz G.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1102-1104
EN
Zero-temperature limits of the local and global thermodynamic quantities in the nine-membered antiferromagnetic s=3/2 spin ring are investigated by means of numerical exact diagonalization. An anisotropic Heisenberg model with tunable bond defect reflecting continuously varying topology (from closed to open ring) is exploited. The frustrated and non-frustrated phases are identified in the ground-state phase diagram determined by a bond-defect strength and magnetic field. Near the phase boundaries significance of the thermal fluctuations affecting the estimates of the local magnetic quantities found earlier at T=1 K is revealed. For the global quantities the effects of thermal fluctuations are found much weaker. A sequence of the local magnetic moments is analysed and their experimental verification at the edges of the non-frustrated and within the entire frustrated phase is suggested at sufficiently low temperature.
9
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Magnetic Properties of the Spin-1 Two-Dimensional J_{1}-J_{3} Heisenberg Model on a Triangular Lattice

63%
Rubin P., Sherman A., Schreiber M.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
242-243
EN
Motivated by the recent experiment in NiGa_{2}S_{4}, the spin-1 Heisenberg model on a triangular lattice with the ferromagnetic nearest- and antiferromagnetic third-nearest-neighbor exchange interactions, J_{1} = -(1 - p)J and J_{3} = pJ, J > 0, is studied in the range of the parameter 0 ≤ p ≤ 1. Mori's projection operator technique is used as a method, which retains the rotation symmetry of spin components and does not anticipate any magnetic ordering. For zero temperature several phase transitions are observed. At p ≈ 0.2 the ground state is transformed from the ferromagnetic order into a disordered state, which in its turn is changed to an antiferromagnetic long-range ordered state with the incommensurate ordering vector Q' ≈ (1.16, 0) at p ≈0.31. With growing p the ordering vector moves along the line Q'-Q_{c} to the commensurate point Q_{c} = (2π/3, 0), which is reached at p = 1. The final state with the antiferromagnetic long-range order can be conceived as four interpenetrating sublattices with the 120° spin structure on each of them. Obtained results offer a satisfactory explanation for the experimental data in NiGa_{2}S_{4}.
10
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Collective Excitations in Heisenberg Ultrathin Films with Inhomogeneous Spatial Distribution of Magnetisation

63%
Łosiński R., Onyszkiewicz Z.
Acta Physica Polonica A
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2000
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vol. 98
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issue 4
419-428
EN
The influence of non-magnetic substrate on the collective excitation of the Heisenberg (s=1/2) ferromagnetic ultrathin films with homogeneous and inhomogeneous spatial distribution of magnetization is investigated. It has been proved that the collective excitation spectrum of ultrathin film may, to a significant degree, depend on the value of the coefficient characterizing the film coupling with its substrate.
11
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Small Antiferromagnetic Clusters

63%
Buczko R., Wilamowski Z., Jantsch W.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
747-750
EN
The analysis of the quantum mechanical model of mesoscopic size antiferromagnets shows that small antiferromagnets are characterized by a stronger exchange coupling and by an oscillating character of spins polarizations. Experimental evidence of the quantum character is discussed. We interpret the interlayer coupling in antiferromagnet superlattices and a puzzling resonance observed in nano-size antiferromagnet grains.
12
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Spin-1/2 XXZ Diamond Chain within the Jordan-Wigner Fermionization Approach

63%
Verkholyak T., Strečka J., Jaščur M., Richter J.
Acta Physica Polonica A
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2010
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vol. 118
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issue 5
978-979
EN
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.
13
Content available remote

An Extended Supersymmetric t-J Model

63%
Zhang Y.-Z.
Acta Physica Polonica A
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1995
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vol. 88
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issue 6
1119-1122
EN
A new lattice model is presented for correlated electrons on the un­restricted 4^{L}-dimensional electronic Hilbert space ⨁^{L}_{n=1}C^{4} (where L is the lattice length). It is an extension of the supersymmetric t-J model. The new model has gl(2|1) supersymmetry and contains one symmetry-preserving free real parameter α which has its origin in the one-parameter family of inequiv­alent typical 4-dimensional irreps of gl(2|1). When α = 0, the model reduces to the supersymmetric t-J model.
14
Content available remote

Solitons in a Compressible Heisenberg Chain

63%
Lipiński S.
Acta Physica Polonica A
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1994
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vol. 85
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issue 2
367-370
EN
Nonlinear excitations in a Heisenberg chain coupled to the lattice in the presence of an external field are studied within a semi-classical approach.
15
Content available remote

Localized Spin Relaxation Due To Coupling To Effective Mass States

63%
Wilamowski Z., Dmochowski J., Jantsch W.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 5
1055-1058
EN
The EPR of residual Mn in CdF_{2} doped with Y, In and Ga is investigated. Although these donors are barely seen in EPR, they manifest themselves by a new effect: a drastic resonant reduction in the longitudinal relaxation rate of Mn which occurs only if the Zeeman splitting of the two subsystems coincide. In this situation, the saturation of those of the six Mn hyperfine lines is weakened which coincide with the shallow donor resonance.
16
Content available remote

Matrix Representation of Constants of Motion for One-Dimensional Heisenberg Magnet

63%
Jakubczyk P., Labuz M., Lulek T.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2
176-178
EN
We demonstrate an exact diagonalization of the one-dimensional Heisenberg magnet in terms of algebraic Bethe Ansatz. We point out, by a polynomial expansion of the transfer matrix with respect to spectral parameter, a complete set of observables for classification of all eigenstates. We introduce an application of our approach on the example of the Heisenberg magnet consisting of four qubits, including its constants of motion, density matrices and complete classification of eigenstates.
17
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The Energy Spectrum and Thermodynamics of Spin-1/2 XX Chain with Ising Impurities

63%
Ezerskaya E.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
928-930
EN
The energy spectrum and peculiarities of field and temperature dependences of the basic thermodynamic characteristics of the finite spin-1/2 XX chain closed by one zz (Ising) bond and open ends XX-chain with two zz-impurities at the both ends have been investigated.
18
Content available remote

Quantum Phenomena in Small Antiferromagnets

63%
Wilamowski Z., Buczko R., Jantsch W.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 2
379-382
EN
We show that the most characteristic properties of mesoscopic antiferromagnets can be explained in terms of the response on a spatially inhomogeneous perturbation. This concept allows to explain the dynamic properties (quantum resonance, coherence and tunnelling rates) as well as static perturbations which, for increasing size of an antiferromagnet, leads to a transition from the quantum mechanical oscillating system to a classical antiferromagnet with well defined Néel vectors.
19
Content available remote

Combinatorics of Lax Objects in Bethe Ansatz

63%
Stagraczyński R.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2
216-218
EN
Algebraic Bethe Ansatz, also known as quantum inverse scattering method, is a consistent tool based on the Yang-Baxter equation which allows to construct Bethe Ansatz exact solutions. One of the most important objects in algebraic Bethe Ansatz is a monodromy matrix M̂, which is defined as an appropriate product of so-called Lax operators L̂ (local transition operators). Monodromy matrix as well as each of Lax operators acts in the tensor product of the quantum space 𝓗 with an auxiliary space ℂ². Thus M̂, when written in the standard basis of auxiliary space, consists of four elements Â, B̂, Ĉ, D̂, which are the operators acting in quantum space 𝓗, where B̂ and Ĉ are step operators and the remaining generate all constants of motion. In this work a consistent method of construction of the Bethe Ansatz eigenstates in terms of objects â, b̂, ĉ, d̂ i.e. matrix elements of the Lax operators in the auxiliary space is proposed.
20
Content available remote

Dynamic Correlations in a Random Spin-1/2 XY Chain

63%
Verkholyak T., Derzhko O., Krokhmalskii T., Stolze J.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
441-444
EN
We examine dynamic quantities of a random spin-1/2 isotropic XY chain in a transverse field. The randomness is related to the sign of the nearest-neighbor exchange interaction and can be eliminated by a suitable transformation. As a result, the dynamic quantities for the random spin chain are related to the same dynamic quantities for the homogeneous spin chain. We use the available results for the latter model to discuss the effect of randomness on the dynamic structure factors of the quantum spin chain.
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