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Wyświetlanie 1-15 z 39
Tytuł:
Applications of Density Matrix Renormalization Group to Problems in Magnetism
Autorzy:
Gehring, G. A.
Bursill, R. J.
Xiang, T.
Powiązania:
https://bibliotekanauki.pl/articles/1953163.pdf
Data publikacji:
1997-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
11.10.Gh
Opis:
The application of real space renormalization group methods to quantum lattice models has become a topic of great interest following the development of the density matrix renormalization group by White. This method has been used to find the ground and low-lying excited state energies and wave functions of quantum spin models in which the form of the ground state is not clear, for instance because the interactions are frustrated. It has also been applied to fermion problems where the tendency for localization due to the strong Coulomb repulsion is opposed by the lowering of the kinetic energy which occurs as a result of electron transfer. The approach is particularly suitable for one-, or quasi-one-dimensional problems. The method involves truncating the Hilbert space in a systematic and optimised manner. Results for the ground state energy are thus variational bounds. The results for low-lying energies and correlation functions for one-dimensional systems have unprecedented accuracy and the method has become the method of choice for solving one-dimensional quantum spin problems. We review the method and results obtained for the spin-1 chain with biquadratic exchange as well as the spin-1/2 model with competing nearest and next nearest neighbour exchange will be described. More recently, the density matrix renormalization group has been applied to reformulate the coupling constant renormalization group approach which is appropriate for the study of critical properties. This approach has been applied to the anisotropic spin-1/2 Heisenberg chain. Finally, we discuss recent work which has borne promising applications in two dimensions - the Ising model and the two-dimensional Hubbard model.
Źródło:
Acta Physica Polonica A; 1997, 91, 1; 105-119
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Asymmetry Driven Phase Transformations
Autorzy:
Damczyk, J.
Ostasiewicz, K.
Radosiński, Ł.
Radosz, A.
Powiązania:
https://bibliotekanauki.pl/articles/1535592.pdf
Data publikacji:
2010-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.70.-a
64.60.-i
63.70.+h
Opis:
Motivated by the properties of one-dimensional lattice systems with asymmetric on-site potential, one can formulate a hypothesis of an asymmetry driven phase transformation. Characteristic feature of one-dimensional systems exhibiting asymmetry driven phase transformation is a sequence of the two phase conversions. In particular class of such systems with a triple-well potential, phase conversions of one-dimensional systems would evolve into a sequence of two phase transitions in three-dimensional models. We propose here a model of three-dimensional system exhibiting a sequence of two first order asymmetry driven phase transitions.
Źródło:
Acta Physica Polonica A; 2010, 118, 4; 527-530
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Behaviors of Phase Diagrams of Ising Model with Competing Ternary and Binary Interactions on a Cayley Tree of Arbitrary Order
Autorzy:
Akin, H.
Ganikhodjaev, N.
Uguz, S.
Temir, S.
Powiązania:
https://bibliotekanauki.pl/articles/1490877.pdf
Data publikacji:
2012-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.50.+q
64.60.-i
64.60.De
Opis:
An Ising model with competing interactions has recently been studied extensively because of the appearance of nontrivial magnetic orderings. In this paper, we study the phase diagrams for the Ising model on a Cayley tree with competing nearest-neighbor interactions J and ternary prolonged interactions $J_{t_{p}}$ on a Cayley tree of arbitrary order k and compare with the phase diagrams obtained in Uguz et al. and Vannimenus results for the Ising model on a Cayley tree with competing nearest-neighbor interactions J and ternary prolonged interactions $J_{p}$. For some values of k, we obtain phase diagrams of the model. We clarify the role of order k of the Cayley tree. We also plot the variation of the wave vector with temperature.
Źródło:
Acta Physica Polonica A; 2012, 121, 1; 104-107
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chemical Potential Derivative as Hallmark for Phase Transitions
Autorzy:
Pietruszka, M.
Matlak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2011158.pdf
Data publikacji:
1999-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
75.40.Cx
75.50.Ee
Opis:
We study antiferromagnetic properties of the two-band extended s-f model with fluctuating valence in the context of two mutually bound new effects of chemical potential critical behaviour, as well as of critical electron redistribution. In order to exemplify both phenomena we build phase diagrams of the system displaying the dependence of the critical Néel temperatures (T$\text{}_{N}$) of the system versus 4f (5f) level positions. The phase diagram consists of two different areas corresponding to antiferromagnetic and paramagnetic phases. We plot the magnetizations and the correlation functions of the system as functions of temperature. Next, we investigate the temperature dependence of the relative average occupation numbers Δn$\text{}^{f(d)}$ and the chemical potential Δμ for a given 4f (5f) level position E$\text{}_{f}$. Plotting this quantities along the E$\text{}_{f}$ cross-section lines we observe small (of the order of 10$\text{}^{-4}$-10$\text{}^{-3}$) but well localized kinks exactly at the Néel temperature T$\text{}_{N}$. Last but not least, we plot the first derivative of the chemical potential dμ/dT which, as it shows clearly visible jumps at T$\text{}_{N}$, may turn out to be very accurate and sensitive (auxiliary) tool to find critical temperatures of the considered system. Moreover, we plot the difference μ$\text{}_{AF}$-μ$\text{}_{PARA}$ where we subtract a chemical potential value of a reference paramagnetic sample from the actual value of the antiferromagnetic system. Also in this case we report the observation of discontinuous change in slope at T$\text{}_{N}$. Our observations can be extended to point out to a new practical possibility of how to find experimentally the critical temperatures of the antiferromagnetic systems exclusively from the chemical potential measurements. We expect that the same type of measurement, according to our recent and present results, would also apply to all types of critical phenomena in real solids.
Źródło:
Acta Physica Polonica A; 1999, 96, 6; 725-732
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Critical Behaviour of Some 2D Lattice Models
Autorzy:
Kamieniarz, G.
Blöte, H. W.J.
Dekeyser, R.
Powiązania:
https://bibliotekanauki.pl/articles/1930586.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.50.+q
64.60.-i
64.60.Cn
64.60.Ak
64.60.Fr
75.40.Mg
Opis:
The density series of the non-interacting hard-square lattice gas model are reanalyzed by the ratio, Dlog Padé and differential approximant methods. The problem of poor consistency between series and other results is resolved. Transfer matrix calculations are performed, implementing both finite-size scaling and conformal invariance. Very accurate estimates of the critical exponents y$\text{}_{t}$, and y$\text{}_{h}$ are obtained in agreement with Ising universality. Furthermore, an improvement of the value of the critical density ρ$\text{}_{c}$ is found. In addition, the universal critical-point ratios of the square of the second and the fourth moment of the magnetization for ferromagnetic Ising models on the square and on the triangular lattice with periodic boundary conditions are reported.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 389-393
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Description of Extreme Gibbs Measures for the Ising Model with Three Interactions
Autorzy:
Akin, H.
Ganikhodjaev, N.
Temir, S.
Uguz, S.
Powiązania:
https://bibliotekanauki.pl/articles/1400048.pdf
Data publikacji:
2013-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
05.50.+q
64.60.-i
64.60.De
75.10.Hk
Opis:
In this paper, we consider an Ising model with three competing interactions (nearest neighbor, next-nearest neighbor, and ternary prolonged neighbor) on the Cayley tree of order two, investigated by Ganikhodjaev et al. We study translation-invariant Gibbs measures of the Ising model with these competing interactions. Also, we investigate the set of the extreme Gibbs measures called Markov random fields with memory 2 of the model.
Źródło:
Acta Physica Polonica A; 2013, 123, 2; 484-487
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Earth Materials at High Pressure and Temperature: Recent Contributions from in situ Synchrotron X-Ray Diffraction
Autorzy:
Redfern, S. A. T.
Powiązania:
https://bibliotekanauki.pl/articles/1963306.pdf
Data publikacji:
1997-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
07.35.+k
91.35.-x
Opis:
The application of synchrotron X-ray powder diffraction to the study of minerals and understanding of the structure and dynamics of the Earth's deep interior is summarised. The salient features of the diamond anvil cell and large-volume multi-anvil cell high-P/T apparatus as used at synchrotron radiation sources are described, and recent developments and applications of these techniques within high-P/T mineralogy are reviewed.
Źródło:
Acta Physica Polonica A; 1997, 91, 4; 659-668
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electric and Magnetic Properties of Hydrogels Doped with Cu Ions
Autorzy:
Coşkun, R.
Okutan, M.
Yalçın, O.
Kösemen, A.
Powiązania:
https://bibliotekanauki.pl/articles/1418231.pdf
Data publikacji:
2012-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
52.25.Mq
82.35.-x
42.70.Jk
64.60.-i
76.30.-v
Opis:
The electric and magnetic properties of Cu doped and pure/undoped hydrogels were investigated by impedance spectroscopy and electron spin resonance techniques, respectively. The capacitance and dissipation factor (tan δ) were measured in the frequency range of 100 Hz-10 MHz at room temperature. The Cole-Cole plots for the Cu doped dry and pure dry hydrogels have been used to describe the characteristic change of electrical properties in mentioned temperature interval. The comparison between Cu ions doped and pure/undoped samples is done using the impedance spectroscopy and the electron spin resonance techniques. Electron spin resonance signal for pure, Cu doped wet and Cu doped dry samples are not any power absorption signal, near the symmetric with respect to the resonance field values according to the dry sample and asymmetric for resonance field/base line, respectively.
Źródło:
Acta Physica Polonica A; 2012, 122, 4; 683-687
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electromagnetic Waves Generation in $Ni_{2.14}Mn_{0.81}GaFe_{0.05}$ Heusler Alloy at Structural Phase Transition
Autorzy:
Bychkov, I.
Kuzmin, D.
Kalenov, D.
Kamantsev, A.
Koledov, V.
Kuchin, D.
Shavrov, V.
Powiązania:
https://bibliotekanauki.pl/articles/1387405.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
75.50.Cc
Opis:
Electromagnetic waves generated by the Heusler alloy $Ni_{2.14}Mn_{0.81}GaFe_{0.05}$ at structural phase transition was detected in the frequency range of 28-32 GHz. Influence of the kinetics of phase transitions on the nature of the sample millimeter radiation was studied as well. It has been observed that the contribution of the intrinsic radiation increases with increasing of the heating/cooling rate. The possible mechanisms and theory of such effect is discussed. It is shown that the maximum radiation intensity should be emitted in direction perpendicular to the movement of interphase boundary.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 588-590
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Embedded Atom Method for Theoretical Strength and Stability of Some fcc Metals
Autorzy:
Öztekin Çiftci, Y.
Çolakoğlu, K.
Powiązania:
https://bibliotekanauki.pl/articles/2028900.pdf
Data publikacji:
2001-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
62.20.-x
Opis:
The structural phase transformation and theoretical strength of fcc metals Ni, Cu, Ag, Al, Au, and Pt under [100] uniaxial loading are studied by using analytical embedded-atom-potential method. In the present calculations the stress-free bcc phase is found unstable and fcc phase is found to be stable. The obtained energy differences of fcc-bcc phases are comparable with those found by the first-principles calculations and experiments for all metals considered. The present pair potential in the embedded-atom method is used for the first time for this purpose. Theoretical lattice parameters, volumes, and energies of the bcc and fcc structures for each metal at zero pressure are calculated and compared with the available experimental values. Third-order elastic constants and pressure-volume curves for studied metals are also investigated and found generally good agreement with experiments.
Źródło:
Acta Physica Polonica A; 2001, 100, 4; 539-551
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
EPR Study of Monoclinic RbD$\text{}_{2}$PO$\text{}_{4}$ Monocrystal Doped with Cr$\text{}^{5+}$ Ion
Autorzy:
Waplak, S.
Shuvalov, L. A.
Powiązania:
https://bibliotekanauki.pl/articles/1932129.pdf
Data publikacji:
1995-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
76.30.-v
64.60.-i
Opis:
Deuterated monoclinic RbD$\text{}_{2}$PO$\text{}_{4}$ (DRDP) doped with chromium Cr$\text{}^{5+}$ is studied by EPR in 90 K to 400 K temperature range. EPR reveals two types of paramagnetic centers: single Cr$\text{}^{5+}$ (S = 1/2) complex and Cr$\text{}^{5+}$-Cr$\text{}^{5+}$ coupled pairs with effective spin S = 1. The EPR line splitting of single Cr$\text{}^{5+}$ complex in DRDP versus temperature agrees with the unit cell multiplication. The splitting of EPR line of pair spectrum appears at T* = 160 K, far below the phase transition temperatures and is due to the anisotropy of the exchange interaction. The clustering effect in the low-dimensional DRDP is suggested.
Źródło:
Acta Physica Polonica A; 1995, 87, 3; 643-648
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Excitonic Instabilities of Deformable Lattice - from Self-Trapping to Phase Transition
Autorzy:
Toyozawa, Y.
Powiązania:
https://bibliotekanauki.pl/articles/1931862.pdf
Data publikacji:
1995-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
71.35.+z
71.38.+i
Opis:
The optically created exciton will be self-trapped if its coupling to phonons is strong enough, and will moreover be self-decomposed if the electron and the hole couple to phonons in an opposite way. The bistability between the parity-conserved and parity-broken self-trapped excitons was observed in alkali halides. The situation is most dramatic if the bistability between the parity-broken self-trapped exciton and the ground state (with no exciton) comes into play since the electron-hole pairs may then be spontaneously generated at every lattice site, resulting in the electronic and structural phase transition. The neutral to ionic phase transition observed in a few organic charge transfer compounds under applied pressure or decreasing temperature can be considered as an example. Recent experiment revealed that TTF-chloranil, among others, is subject to photo-induced transient phase change over hundreds of unit cells per one photon. The dynamics of this process can be described in terms of self-trapping and self-multiplication of a photo-generated charge transfer exciton along the chain through the attractive dipolar interaction. This description of phase transition in terms of exciton dynamics will provide a new paradigm of materiology.
Źródło:
Acta Physica Polonica A; 1995, 87, 1; 47-56
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Frustration and Entanglement in Compass and Spin-Orbital Models
Autorzy:
Oleś, Andrzej
Powiązania:
https://bibliotekanauki.pl/articles/1384027.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
64.70.Tg
75.25.Dk
79.60.-i
Opis:
We review the consequences of intrinsic frustration of the orbital superexchange and of spin-orbital entanglement. While the Heisenberg perturbing interactions remove frustration in the compass model, the lowest columnar excitations are robust in the nanoscopic compass clusters and might be used for quantum computations. Entangled spin-orbital states determine the ground states in some cases, while in others concern excited states and lead to measurable consequences, as in the RVO₃ perovskites. On-site entanglement for strong spin-orbit coupling generates the frustrated Kitaev-Heisenberg model with a rich magnetic phase diagram on the honeycomb lattice. Frustration is here reflected in hole propagation which changes from coherent in an antiferromagnet via hidden quasiparticles in zigzag and stripe phases to entirely incoherent one in the Kitaev spin liquid.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 163-169
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Growth Dynamics of Photoinduced Phase Domain in Cyano-Complex Studied by Boundary Sensitive Raman Spectroscopy
Autorzy:
Asahara, A.
Nakajima, M.
Fukaya, R.
Tokoro, H.
Ohkoshi, S.
Suemoto, T.
Powiązania:
https://bibliotekanauki.pl/articles/1490049.pdf
Data publikacji:
2012-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
64.60.-i
82.50.Hp
78.30.-j
Opis:
Rubidium manganese hexacyanoferrate exhibits charge transfer phase transition from high temperature phase to low temperature phase at 230 K. This phase transition can also be triggered by light irradiation resonantly inducing charge transfer from $Mn^{2+}$ to $Fe^{3+}$. In the present study, boundary sensitive Raman spectroscopy was performed for $Rb_{0.94}Mn[Fe(CN)_6]_{0.98} \cdot 0.2H_2O$ in both cases of photoinduced and thermal phase transition. Since the frequencies of C ≡ N stretching vibration modes are very sensitive to the valence states of the adjacent metal ions, we can quantify the distribution of not only high and low temperature phase but also boundary configurations from the observed spectra. We obtained the time evolution of the fraction ratios of the valence states from the observed peak areas. In the case of photoinduced situation, the boundary increases up to 15% when high temperature phase diminishes to 55% of the initial fraction. This is quite different from the result in thermal phase transition where the boundary is created only 0.8% at the same high temperature phase fraction value. We conclude that many small domains are preferably created in photoinduced phase transition since the ratio of boundary is large, while large domains grow in thermal phase transition.
Źródło:
Acta Physica Polonica A; 2012, 121, 2; 375-384
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Heat Capacity and Elastic Constants of Fe$\text{}_{3-x}$Zn$\text{}_{x}$O$\text{}_{4}$ in the Vicinity of the Verwey Transition
Autorzy:
Kozłowski, A.
Kąkol, Z.
Schwenk, H.
Bareiter, S.
Hinkel, C.
Luthi, B.
Honig, J. M.
Powiązania:
https://bibliotekanauki.pl/articles/2013722.pdf
Data publikacji:
2000-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
62.20.Dc
63.20.-e
64.60.-i
65.40.+g
Opis:
The results of the heat capacity and elastic constant studies of Fe$\text{}_{3-x}$Zn$\text{}_{x}$O$\text{}_{4}$ (x<0.04) series are reported. Adiabatic heat capacity measurements, performed on single crystals, show the clear change of the transition character from first order for low Zn content (x<0.012) to the higher order in 0.012
Źródło:
Acta Physica Polonica A; 2000, 97, 5; 883-887
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 39

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