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Wyświetlanie 1-15 z 5347
Tytuł:
Orbital Correlations in Monolayer Manganites - From Spin t-J Model to Orbital t-J Model
Autorzy:
Daghofer, M.
Oleś, A. M.
Powiązania:
https://bibliotekanauki.pl/articles/2047308.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
75.10.Jm
75.30.Et
75.47.Lx
Opis:
On the example of monolayer manganites we show that the theoretical ideas developed long ago along the derivation of the spin t-J model from the Hubbard model are nowadays very helpful in strongly correlated oxides with partly filled degenerate orbitals. We analyze a realistic orbital t-J model for e$\text{}_{g}$ electrons in La$\text{}_{1-x}$Sr$\text{}_{1+x}$MnO$\text{}_{4}$ monolayer manganites, and discuss the evolution of spin and orbital correlations under increasing doping by performing exact diagonalization of finite clusters, with electronic kinetic energy determined self-consistently at a finite temperature by classical Monte Carlo for t$\text{}_{2g}$ spins. Several experimental results are reproduced.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 497-512
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
An Extended Supersymmetric t-J Model
Autorzy:
Zhang, Yao-Zhong
Powiązania:
https://bibliotekanauki.pl/articles/1943941.pdf
Data publikacji:
1995-12
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.20.Ad
75.10.Jm
Opis:
A new lattice model is presented for correlated electrons on the unrestricted 4$\text{}^{L}$-dimensional electronic Hilbert space ⨁$\text{}_{n=1}^{L}$C$\text{}^{4}$ (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.
Źródło:
Acta Physica Polonica A; 1995, 88, 6; 1119-1122
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Critical Values for Electron Pairing in t-U-J-V and t-J-V Models
Autorzy:
Bak, M.
Powiązania:
https://bibliotekanauki.pl/articles/1812342.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.20.Fg
74.20.Rp
74.25.Dw
71.10.Fd
71.27.+a
Opis:
The critical values for pairing of s*- and d-wave symmetry are calculated within the t-U-J-V and the t-J-V models in renormalized mean field theory. It is shown that the first model yields the proper critical values in the low density limit while the other does not. Renormalized mean field theory strongly decreases the absolute value of (negative) critical values for larger electron densities.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 275-279
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The t-J Model in a Strong Magnetic Field
Autorzy:
Sherman, A.
Powiązania:
https://bibliotekanauki.pl/articles/1384828.pdf
Data publikacji:
2015-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
71.27.+a
71.70.Di
74.72.Gh
Opis:
The normal-state energy spectrum of the two-dimensional t-J model in a homogeneous perpendicular magnetic field B is investigated using the Mori projection operator technique. The density of states at the Fermi level as a function of 1/B reveals both high- and low-frequency oscillations. The high-frequency oscillations correspond to large Fermi surfaces, while the low-frequency components are related to van Hove singularities in the Landau subbands, which stem from their bending due to strong electron correlations. Frequencies of the low-frequency components are of the same order of magnitude as those observed in underdoped cuprates. These components become dominant if smoothing processes are involved. It is shown that despite increased distances between subbands the pseudogap affects only slightly the frequency of density of states oscillations.
Źródło:
Acta Physica Polonica A; 2015, 127, 2; 213-215
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Magnetic Phases and Generalized t-J Models in Doped Mott-Hubbard Insulators
Autorzy:
Oleś, A. M.
Zaanen, J.
Powiązania:
https://bibliotekanauki.pl/articles/1861025.pdf
Data publikacji:
1994-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.72.-h
64.60.-i
64.90.+b
75.40.-s
Opis:
We review some recent results obtained for the dynamics of a single hole and for the ground states at finite hole doping in t-J model. Next, we address the role of orbital degeneracy in doped Mott-Hubbard insulators and show examples of effective strong coupling models which include the orbital degrees of freedom. These new t-J models have interesting phase diagrams, with the new magnetic phases stabilized by a competition between magnetic energy and excitonic excitations. It is argued that the doped holes always bind to the excitons and that the new phases identified on the mean-field level give rise to local distortions of the lattice. We conclude that realistic t-J models derived from the electronic structure of particular compounds may be successfully applied for understanding both the observed magnetic ground states, and the results of photoemission experiments, as we have demonstrated recently for NiO.
Źródło:
Acta Physica Polonica A; 1994, 85, 1; 145-163
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Quantifying the Suitability of Reference Signals for the Video Streaming Analysis for IPTV
Autorzy:
Hoppe, C.
Manzke, R.
Rompf, M.
Uhl, T.
Powiązania:
https://bibliotekanauki.pl/articles/307690.pdf
Data publikacji:
2016
Wydawca:
Instytut Łączności - Państwowy Instytut Badawczy
Tematy:
communication network
IPVT service
ITU-T J.247
measurement tools
PEVQ
QoS/QoE determination
reference signal
Triple Play Services
VQuad-HD
ITU-T J.341
Opis:
IP networks are indispensable nowadays and they are some of the most efficient platforms. The constantly growing number of users and new services in these networks – the largest being the Internet – require a satisfactory quality of service from any application they use. So, determining the QoS in real-time services is particularly important. This work shows how to quantify the suitability of reference signals for analyzing the quality of video streaming in IPTV. The assessment relies on two different algorithms: PEVQ and VQuad-HD. Three different reference signals – two real ones and an artificial one – are used in this study, and a numerical measurement system is used, which simulates mean network impairments. These measurements provide valuable information for determining the QoS of actual IPTV services in practice.
Źródło:
Journal of Telecommunications and Information Technology; 2016, 1; 29-36
1509-4553
1899-8852
Pojawia się w:
Journal of Telecommunications and Information Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
t-J Model Then and Now: a Personal Perspective from the Pioneering Times
Autorzy:
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2047299.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
74.72.-h
71.10.Fd
Opis:
In this overview we sketch briefly the path to the so-called t-J model derived for the first time 30 years ago and provide its original meaning within the theory of strongly correlated magnetic metals with a non-Fermi (non-Landau) liquid ground state. An emergence of the concept of real space pairing is discussed in a historical prospective. A generalization of this model to the many-orbital situation is briefly discussed. The emphasis is put on didactical exposition of ideas, as they were transformed into mathematical language. The concept of hybrid pairing is introduced in the same context at the end.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 409-424
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
t-t-J-U Model in Mean-Field Approximation: Coexistence of Superconductivity and Antiferromagnetism
Autorzy:
Abram, M.
Powiązania:
https://bibliotekanauki.pl/articles/1374335.pdf
Data publikacji:
2014-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
74.25.Dw
74.72.Gh
Opis:
We discuss the t-J-U model in the mean-field approximation. The role of spin-exchange coupling J and the second nearest hopping t' are examined in the context of the coexistence of superconductivity and antiferromagnetism. Stability of the phases is studied with respect to temperature. The coexistence region exists for the sufficiently large Coulomb repulsion (U>$U_{cr}$), and in the vicinity of the half-filled band (hole doping δ < $δ_{cr}$). The critical hole doping is relatively small ($δ_{cr}$ ≈ 0.006 for J/|t| = 1/3) and linear with respect to J. The decrease of $U_{cr}$ is proportional to J, except the limit of small J (J/|t| < 0.03), where $U_{cr}$ grows rapidly with decreasing J. The effect of the second nearest hopping is limited - the phase diagram does not change in a qualitative manner when the t' value is changed. In the limit of T → 0, SC phase is stable even for large hole-doping (such as δ = 0.5). Additional paramagnetic phase appears for large δ or small U at non-zero temperature. When temperature increases, both SC and AF+SC phase regions are reduced.
Źródło:
Acta Physica Polonica A; 2014, 126, 4a; A-25-A-29
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Reiters Polaron Wave Function Applied to a t_{2_g} Orbital t-J Model
Autorzy:
Wohlfeld, K.
Oleś, A.
Daghofer, M.
Horsch, P.
Powiązania:
https://bibliotekanauki.pl/articles/1810332.pdf
Data publikacji:
2009-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
75.30.Ds
71.38.-k
72.10.Di
Opis:
Using the self-consistent Born approximation we calculate Reiter's wave function for a single hole introduced into the undoped and orbitally ordered ground state of the t-J model with $t_{2g}$ orbital degrees of freedom. While the number of excitations is similar to the spin t-J model for a given J/t, a distinct structure of the calculated wave function and its momentum dependence is identified suggesting the formation of a novel type of mobile polarons.
Źródło:
Acta Physica Polonica A; 2009, 115, 1; 110-113
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
d-Wave Superconductivity, Orbital Magnetism, and Unidirectional Charge Order in the t-J Model
Autorzy:
Raczkowski, M.
Powiązania:
https://bibliotekanauki.pl/articles/1812281.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.72.-h
74.20.Mn
74.81.-g
75.40.Mg
Opis:
Recent scanning tunneling microscopy in the superconducting regime of two different cuprate families revealed unidirectional bond-centered modulation in the local electronic density of states. Motivated by this result we investigate the emergence of modulated d-wave superconductivity coexisting with charge domains that form along one of the crystal axes. While detailed stripe profiles depend on the used form of the Gutzwiller factors, the tendency towards a valence bond crystal remains robust. We also find closely related stripe phase originating from the staggered flux phase, a candidate for the pseudogap phase of lightly doped cuprates.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 107-114
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Doped Carrier Formulation of the t-J model: Monte Carlo Study of the Anisotropic Case
Autorzy:
Ferraz, A.
Kochetov, E.
Maśka, M.
Mierzejewski, M.
Powiązania:
https://bibliotekanauki.pl/articles/1812319.pdf
Data publikacji:
2008-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.62.Dh
Opis:
We derive a doped carrier representation of the t-J model Hamiltonian. Within this approach the t-J model is described in terms of holes hopping in a lattice of correlated spins, where holes are the carriers doped into the half-filled Mott insulator. This representation of the t-J Hamiltonian is very convenient for underdoped systems since close to half-filling it allows for a controlled treatment of the crucial constraint of no doubly occupied sites. When neglecting the transverse spin-spin interaction, the effective Hamiltonian can be investigated with classical Monte Carlo simulations. We discuss the results obtained for systems consisting of several hundred lattice sites.
Źródło:
Acta Physica Polonica A; 2008, 114, 1; 185-189
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 5347

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