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    Wyświetlanie 1-45 z 45
    Tytuł:
    Hybridization Effects in UCu$\text{}_{5-x}$Au$\text{}_{x}$ Compounds
    Autorzy:
    Tran, V. H.
    Troć, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1929857.pdf
    Data publikacji:
    1994-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    Opis:
    We review the results of bulk and neutron diffraction measurements on the UCu$\text{}_{5-x}$Au$\text{}_{x}$ system crystallizing in the cubic AuBe$\text{}_{5}$-type structure. The observed properties may be understood in the light of competition between Kondo effect and RKKY exchange interactions. Effects of 5f-ligand hybridization between the U-atoms occupying the 4a-sites and the Au- or/and Cu-atoms placed at the 4c- and 16e-positions, respectively, are supposed to be different. We show that the prefential occupation of 4c-sites by Au has a marked effect on the magnetic properties of the investigated system.
    Źródło:
    Acta Physica Polonica A; 1994, 85, 2; 287-292
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Transport and Magnetic Properties of Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te Doped with Cr and Mo
    Autorzy:
    Artamkin, A. I.
    Kozhanov, A. E.
    Arciszewska, M.
    Dobrowolski, W. D.
    Story, T.
    Slynko, E. I.
    Slynko, V. E.
    Khokhlov, D. R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2038231.pdf
    Data publikacji:
    2004-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    Opis:
    Transport and magnetic properties of Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te (x<0.18) semiconductor alloys doped with Cr or Mo are investigated in a broad range of temperatures and magnetic fields. In PbMnTe(Cr) alloys the Fermi level may be pinned either in the conduction band or in the energy gap, depending on Mn concentration. In PbMnTe(Mo) alloys the pinning of the Fermi level is observed in the valence band as well as in the energy gap. In the latter case persistent photoconductivity is observed at low temperatures. The analysis of the temperature dependence of magnetic susceptibility shows that PbMnTe alloys doped with Cr or Mo are Curie-Weiss paramagnets revealing weak antiferromagnetic interactions between magnetic ions.
    Źródło:
    Acta Physica Polonica A; 2004, 106, 2; 223-231
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetic-Form Factor Measurements by Polarised Neutron Scattering: Application to Heavy Fermion Superconductors
    Autorzy:
    Neumann, K.-U.
    Ziebeck, K. R. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1929383.pdf
    Data publikacji:
    1993-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.25.+z
    71.28.+d
    Opis:
    The experimental technique of spin polarised neutron scattering as used in magnetic form factor measurements is presented. An introduction to the interpretation and the calculation of magnetic form factors and magnetization densities is given. The experimental technique of neutron scattering theory as applied to elastic spin polarised scattering experiments is briefly introduced. The calculation of the magnetic form factor and the magnetization densities are considered for simple model systems such as a collection of localised magnetic moments or an itinerant electron system. The discussion is illustrated by an experimental investigation of the magnetic form factor in the heavy fermion superconductors UBe$\text{}_{13}$ and UPt$\text{}_{3}$. Magnetization density maps and magnetic form factors are presented, and their implications for other physical quantities are briefly discussed.
    Źródło:
    Acta Physica Polonica A; 1993, 84, 1; 43-81
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Strongly Correlated Electrons in a Magnetic Field: Fermi Liquid versus Spin Liquid
    Autorzy:
    Spałek, J.
    Wójcik, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1930575.pdf
    Data publikacji:
    1994-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.-d
    75.10.Lp
    Opis:
    We compare the Fermi liquid (FL) and statistical spin liquid (SSL) representations of the electronic properties for strongly correlated systems. In particular, we discuss the entropy, as well as the magnetization as a function of band filling, temperature and magnetic field. These properties are quite different in the two (FL, SSL) states. Antiferromagnetic state disappears for a small number of holes in the doped Mott insulator.
    Źródło:
    Acta Physica Polonica A; 1994, 85, 2; 357-361
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Low Temperature Transport and Magnetic Properties of SmB$\text{}_{6}$
    Autorzy:
    Gabani, S.
    Flachbart, K.
    Pavlík, V.
    Konovalova, E.
    Paderno, Y.
    Herrmannsdörfer, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/2013029.pdf
    Data publikacji:
    2000-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.20.Hr
    71.28.+d
    Opis:
    We present results of transport and magnetic properties of three single-crystalline samples of the intermediate valence small-gap semiconductor SmB$\text{}_{6}$ at low temperatures. The received resistivity dependences of the samples below 0.5 K exhibit an activated behavior with an energy gap of a few mK. The temperature dependences of the magnetic susceptibility show an increase below 15 K which can be accounted for by impurities, by bare Sm$\text{}^{3+}$ ions or by a small amount of in-gap magnetic 4f$\text{}^{5}$5d$\text{}^{1}$ states.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 3; 419-422
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetic Properties of $UFe_{2+x}$ Prepared by Splat Cooling
    Autorzy:
    Havela, L.
    Miliyanchuk, K.
    Pešička, J.
    Gonçalves, A.
    Waerenborgh, J.
    Pereira, L.
    Šantavá, E.
    Šebek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813628.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    75.50.Bb
    Opis:
    A series od $UFe_{2+x}$ materials was prepared using splat cooling. The Laves phase structure can accommodate up to 0.3 Fe excess, while $T_C$ is enhanced from 172 K to approximately 240 K. Higher Fe concentration leads to the segregation of α-Fe. $\text{}^{57}Fe$ Mössbauer spectroscopy indicates higher Fe magnetic hyperfine fields on Fe nuclei occupying the U sublattice than for the regular Fe sites.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 247-250
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    First-Principles Study of Kondo Insulator $SmB_{6}$
    Autorzy:
    Gmitra, M.
    Čenčariková, H.
    Farkašovský, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1369765.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    71.20.-b
    71.27.+a
    Opis:
    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.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 298-299
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Vertex Corrections to the Electrical Conductivity of the Disordered Falicov-Kimball Model
    Autorzy:
    Pokorný, V.
    Janiš, V.
    Powiązania:
    https://bibliotekanauki.pl/articles/1534607.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.28.+d
    72.10.Fk
    Opis:
    Quantum coherence of elastically scattered lattice fermions is studied. We calculate vertex corrections to the electrical conductivity of electrons scattered either on thermally equilibrated or statically distributed random impurities and we demonstrate that the sign of the vertex corrections to the Drude conductivity is in both cases negative.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 922-923
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Investigation of Mixed Valence State of $Sm_{1-x}B_{6}$ and $Sm_{1-x}La_{x}B_{6}$ by XANES
    Autorzy:
    Gabáni, S.
    Flachbart, K.
    Bednarčík, J.
    Welter, E.
    Filipov, V.
    Shitsevalova, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1371509.pdf
    Data publikacji:
    2014-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Dm
    71.28.+d
    71.27.+a
    Opis:
    We investigated the valence states of samarium ions in Sm deficient $Sm_{1-x}B_{6}$ (x=0.03, 0.05, 0.08, 0.1 and 0.2) sintered samples, in single crystalline solid solutions $Sm_{1-x}La_{x}B_{6}$ (x=0.16, 0.28, 0.4, 0.55 and 0.7) as well as in a $SmB_{6}$ single crystal by X-ray absorption near edge structure (XANES) between 4.2 and 300 K. It was shown that the mixed valence state $v_{Sm}$ of Sm-ions ($v_{Sm}$ ≈ 2.51 for $SmB_{6}$ at 4.2 K) in deficient samples is changed but maintained up to a concentration of 20% of vacancies and up to a concentration of 70% in samples doped with trivalent La-ions, and that in both cases it increases with temperature. On the other hand, the value of $v_{Sm}$ increases with increasing vacancy level, whereas it decreases with increasing $La^{3+}$ substitution. The obtained dependences of Sm-valence in $SmB_{6}$ on vacancy as well as on $La^{3+}$ ion concentration are in good agreement with susceptibility measurements and exact numerical calculation of the spinless Falicov-Kimball model in two dimensions.
    Źródło:
    Acta Physica Polonica A; 2014, 126, 1; 338-339
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron Correlation Phenomena in Selected Transition Metal Oxides
    Autorzy:
    Honig, J. M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1860849.pdf
    Data publikacji:
    1994-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    71.30.+h
    75.10.Lp
    Opis:
    The theory of electron correlation phenomena is reviewed and used to interpret the transport, thermal, or magnetic properties of V_{2}O_{3}, LaNiO_{3} and Fe_{3}O_{4} systems, each of which to a greater or lesser degree displays correlation effects. A rationale is provided for interpreting the various types of phase transitions encountered in the vanadium sesquioxide and magnetite host systems and to show why these are altered by small compositional variations.
    Źródło:
    Acta Physica Polonica A; 1994, 85, 1; 53-77
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground States of the Falicov-Kimball Model Extended by Nonlocal Coulomb Interactions
    Autorzy:
    Čenčariková, H.
    Farkašovský, P.
    Žonda, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813654.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Lp
    71.27.+a
    71.28.+d
    Opis:
    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.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 287-290
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Thermoelectric Power of $CeNi_4Si$ and $YbNi_4Si$ Compounds
    Autorzy:
    Falkowski, M.
    Kowalczyk, A.
    Tran, V.
    Miiller, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813661.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.20.-b
    72.20.Pa
    71.28.+d
    Opis:
    The thermoelectric power was measured from 4.2 to 300 K for $CeNi_4Si$ and $YbNi_4Si$. The thermoelectric power was analysed in the framework of the phenomenological resonance model. According to the model the dominant contribution to thermopower is caused by scattering between electrons of a broad s-band and a narrow f-band with the Lorentzian shape. The electron-hole analogy is reflected in the thermoelectric power behaviour of the investigated compounds.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 303-306
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground States of the Spin-One-Half Falicov-Kimball Model with Hunds Rule Coupling in Two Dimensions
    Autorzy:
    Čenčariková, H.
    Farkašovský, P.
    Tomašovičová, N.
    Žonda, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1810314.pdf
    Data publikacji:
    2009-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Lp
    71.27.+a
    71.28.+d
    Opis:
    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.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 1; 101-103
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Thermodynamics of the Generalized Spin-One-Half Falicov-Kimball Model in Two Dimensions
    Autorzy:
    Žonda, M.
    Farkašovský, P.
    Čenčariková, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/1810315.pdf
    Data publikacji:
    2009-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Lp
    71.27.+a
    71.28.+d
    Opis:
    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.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 1; 104-106
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    X-Ray Resonant Magnetic Scattering: Application to Thin Films and Multilayers
    Autorzy:
    Raoux, D.
    Jaouen, N.
    Tonnerre, J. M.
    Bontempi, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2014370.pdf
    Data publikacji:
    2000-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    78.70.Ck
    71.27.+a
    Opis:
    This paper reports on the use of a new technique to investigate the magnetic properties of thin films, multilayers and artificial structures, the X-ray resonant magnetic scattering at small values of the scattering vector. It can be used either by registering the reflectivity pattern or in a diffraction mode. In comparison with magneto-optical Kerr effect or neutron scattering, it offers an atomic selectivity due to the resonant excitation of a core electron, and even an electronic shell one. Examples are presented mainly in the soft X-range allowing to probe the 3d band of transition metals. They demonstrate the promising possibilities of the method to measure the magnetic moments carried by each of the atomic components in complex systems, as well as their distribution through thin layers, with an atomic resolution.
    Źródło:
    Acta Physica Polonica A; 2000, 98, 5; 483-494
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Manifestation of Electron Correlations in the V$\text{}_{2}$O$\text{}_{3}$ and NiS$\text{}_{2}$ Systems
    Autorzy:
    Honig, J. M.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047302.pdf
    Data publikacji:
    2007-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.30.+h
    71.28.+d
    72.80.Ga
    Opis:
    The experimental manifestation of electron correlation effects in the V$\text{}_{2}$O$\text{}_{3}$ and NiS$\text{}_{2}$ systems are reviewed, and recent elementary theories for interpreting the many different types of metal-insulator transitions based on these theories are provided. Research on the critical phenomena displayed by the interacting electrons in these systems is also reviewed.
    Źródło:
    Acta Physica Polonica A; 2007, 111, 4; 437-454
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    2D Angular Correlation of Annihilation Radiation: Current Trends and Future Possibilities
    Autorzy:
    West, R. N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933550.pdf
    Data publikacji:
    1995-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    71.25.Ηc
    78.70.Bj
    Opis:
    Recent improvements in two-dimensional angular correlation measurement and analysis techniques have greatly increased the power of the method to image the Fermi surfaces of electronically complex systems. That, and the further and dramatic improvement that must result when the present radioisotope positron sources are replaced by intense monoenergetic positron beams are discussed and illustrated.
    Źródło:
    Acta Physica Polonica A; 1995, 88, 1; 249-256
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Two-Band Model for Coherent Excitonic Condensates
    Autorzy:
    Apinyan, V.
    Kopeć, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/1398643.pdf
    Data publikacji:
    2016-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.Fd
    71.28.+d
    71.35.-y
    71.10.Hf
    Opis:
    We consider the excitonic correlations in the two-band solid state system composed of the valence band and conduction band electrons. We treat the phase coherence mechanism in the system by presenting the electron operator as a fermion attached to the U(1) phase-flux tube. The emergent bosonic gauge field, related to the phase variables appears to be crucial for the coherent Bose-Einstein condensation of excitons. We calculate the normal excitonic Green functions, and the single-particle density of states functions being a convolution between bosonic and fermionic counterparts. We obtain the total density of states as a sum of two independent parts. For the coherent normal fermionic density of states, there is no hybridization-gap found in the system due to strong coherence effects and phase stiffness.
    Źródło:
    Acta Physica Polonica A; 2016, 130, 2; 621-624
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconducting Properties and Phase Separation Effects in Systems with Local Pairing
    Autorzy:
    Pawłowski, G.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1955833.pdf
    Data publikacji:
    1997-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.-d
    74.20.-z
    05.30.Jp
    Opis:
    We examine the phase separation effects in a class of models developed for description of superconductors with local electron pairing: (i) the extended attractive Hubbard model, (ii) the model of hard-core charged bosons on a lattice. We analyse the behaviour of various superfluid characteristics as well as the evolution of the phase diagrams with increasing external magnetic field.
    Źródło:
    Acta Physica Polonica A; 1997, 91, 2; 409-413
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    From Weak to Strong Coupling Superconductivity: Collective Modes in a Model with Local Attraction
    Autorzy:
    Kostyrko, T.
    Micnas, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/1929358.pdf
    Data publikacji:
    1993-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    73.20.Mf
    Opis:
    We discuss the density-density response functions and the collective excitation spectrum for the extended Hubbard model with on-site attraction and arbitrary electron density, in the superconducting ground state. For the short-range intersite interaction we find the sound wave-like modes with the velocity interpolating smoothly between the weak (v ∝ 2Zt, |U| ≪ 2Zt) and strong coupling (v ∝ Zt$\text{}^{2}$/|U|,|U| ≫ 2Zt) limits. The latter agrees with the results obtained from an effective pseudospin Hamiltonian valid in the strong coupling limit. In the weak coupling regime, we obtain that apart from a commensurate charge density wave instability, an increase in the intersite Coulomb repulsion can give rise to a charge density wave incommensurate with the lattice period, away from half-filling. The ground state phase diagram for 2D square lattice, including singlet superconducting ground state, electronic droplet formation, and charge density waves is determined. It is also shown that the energy of collective excitations evolves smoothly from weak to strong coupling limit for a 2D lattice, in the case of a long-range Coulomb interaction. Finally, the mode coupling effects in the frequency behavior of the density-density response functions are analyzed.
    Źródło:
    Acta Physica Polonica A; 1993, 83, 6; 837-848
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconductivity of the Two-Dimensional Penson-Kolb Model
    Autorzy:
    Czart, W. R.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2029270.pdf
    Data publikacji:
    2001-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    74.25.Ha
    Opis:
    Two-dimensional (d=2) Penson-Kolb model, i.e. the tight-binding model with the pair-hopping (intersite charge exchange) interaction, is considered and the effects of phase fluctuations on the s-wave superconductivity of this system are discussed within the Kosterlitz-Thouless scenario. The London penetration depth λ at T=0, the Kosterlitz-Thouless critical temperature T$\text{}_{c}$, and the Hartree-Fock approximation critical temperature T$\text{}_{p}$ are determined as a function of particle concentration and interaction. The Uemura type plots (T$\text{}_{c}$ vs.λ$\text{}^{-2}$(0)) are derived. Beyond weak coupling and for low concentrations they show the existence of universal scaling: T$\text{}_{c}$ ~1/λ$\text{}^{2}$(0), as it was previously found for the attractive Hubbard model and for the models with intersite electron pairing.
    Źródło:
    Acta Physica Polonica A; 2001, 100, 6; 885-895
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground State and Thermodynamic Properties of an Induced-Pairing Model
    Autorzy:
    Pawłowski, G.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1992710.pdf
    Data publikacji:
    1998-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    74.25.Ha
    Opis:
    We study the phase diagrams and thermodynamic properties of a system of coexisting wide-band current carriers (c-particles) and narrow-band electrons (d-electrons) which can form local pairs. There are two distinct mechanisms of superconductivity in the model considered: (i) the intersubsystem charge exchange, which leads to the superconducting state involving both types of electrons and (ii) the pair hopping interaction of d-electrons, leading to the superconducting state of d-particles only. In contrast to previous works on the subject, we assume an arbitrary value of on-site density interaction of d-electrons U, which allows us to study the effects of reduced d-pair binding energy. Within the approach in which the U term is exactly treated we determine the evolution of superconducting properties as a function of interactions and relative position of the bands. In a definite range of parameters the system shows features which are intermediate between those of a local pair superconductor and those of a classical BCS model. The increasing on-site Coulomb repulsion U competing with the intersubsystem charge exchange and the pair hopping interaction reduces the superconducting critical temperature. Moreover, it can induce a change of the superconducting transition into the first order one. Above a critical value of U, dependent on concentration of electrons and other interactions, the superconducting state cannot be stable at any temperature.
    Źródło:
    Acta Physica Polonica A; 1998, 94, 4; 683-699
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    $\text{}^{11}$B-NMR Study of $SmB_6$ under Pressure
    Autorzy:
    Pristáš, G.
    Mito, T.
    Kohara, T.
    Gabáni, S.
    Reiffers, M.
    Flachbart, K.
    Takeshita, N.
    Shitsevalova, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1534330.pdf
    Data publikacji:
    2010-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    76.60.-k
    62.50.-p
    71.28.+d
    Opis:
    We present first experimental results of $\text{}^{11}$B-NMR of SmB_6 under applied pressure. From measurement of nuclear spin-lattice relaxation time $(T_1)$ we find that with applied pressure the value of activation gap $E_{g}$ is decreasing. This decrease is larger than in case of other experimental techniques. We suppose that the enhancement of $1//T_1$ in temperature range 20-100 K with applied pressure reflects not only a suppression of hybridization gap, but also changes in spin correlations.
    Źródło:
    Acta Physica Polonica A; 2010, 118, 5; 895-896
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electron Dynamics in Crystalline Semiconductors
    Autorzy:
    Zawadzki, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/1400405.pdf
    Data publikacji:
    2013-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    73.61.Ey
    72.20.-i
    Opis:
    Electron dynamics in crystalline semiconductors is described by distinguishing between an instantaneous velocity related to electron's momentum and an average velocity related to its quasi-momentum in a periodic potential. It is shown that the electron velocity used in the theory of electron transport and free-carrier optics is the average electron velocity, not the instantaneous velocity. An effective mass of charge carriers in solids is considered and it is demonstrated that, in contrast to the "acceleration" mass introduced in textbooks, it is a "velocity" mass relating carrier velocity to its quasi-momentum that is a much more useful physical quantity. Among other advantages, the velocity mass is a scalar for spherical but nonparabolic energy bands ϵ(k), whereas the acceleration mass is not a scalar. Important applications of the velocity mass are indicated. A two-band k·p^ model is introduced as the simplest example of a band structure that still keeps track of the periodic lattice potential. It is remarked that the two-band model, adequately describing narrow-gap semiconductors (including zero-gap graphene), strongly resembles the special theory of relativity. Instructive examples of the "semi-relativistic" analogy are given. The presentation has both scientific and pedagogical aspects.
    Źródło:
    Acta Physica Polonica A; 2013, 123, 1; 132-138
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Far-Infrared Study of DX-Like Centers in Pb$\text{}_{0.95}$Mn$\text{}_{0.05}$Te(Ga)
    Autorzy:
    Stojanović, D.
    Trajić, J.
    Hadžić, B.
    Romčević, M.
    Ivanchik, I. I.
    Khokhlov, D. R.
    Romčević, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047857.pdf
    Data publikacji:
    2007-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    78.20.-e
    63.20.Pw
    Opis:
    We present far-infrared reflection spectra of Pb$\text{}_{0.95}$Mn$\text{}_{0.05}$Te single crystal doped with gallium between 10 and 300 K. The analysis of the far-infrared reflection spectra was made by a fitting procedure based on the model of coupled oscillators. Together with the strong plasmon-phonon coupling we obtain three local modes of gallium at about 122 cm$\text{}^{-1}$, 166 cm$\text{}^{-1}$, and 192 cm$\text{}^{-1}$. The position of these modes depends on impurity center charge, and their intensity depends on temperature.
    Źródło:
    Acta Physica Polonica A; 2007, 112, 5; 959-962
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Spectral Properties and New Interpolating Solution of Anderson Model
    Autorzy:
    Kuzemsky, A. L.
    Powiązania:
    https://bibliotekanauki.pl/articles/1964660.pdf
    Data publikacji:
    1997-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    67.40.Db
    71.28.+d
    75.20.Hr
    Opis:
    A new approach to many-body quasiparticle dynamics of the Anderson impurity model at finite temperatures is proposed in the framework of the equation-of-motion method. We find a new exact identity, which relates the one-particle and many-particle Green functions. Using this identity, it is shown that a new interpolating approximation for the one-particle Green function can be constructed. The approximation which simultaneously reproduces the weak-coupling limit and the strong coupling limit can be formulated self-consistently. This approach offers a new method for a systematic construction of the approximate interpolating dynamical solutions of strongly correlated electron models.
    Źródło:
    Acta Physica Polonica A; 1997, 92, 2; 355-358
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pseudospin Models of Superconductors with Very Short Coherence Length
    Autorzy:
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1860991.pdf
    Data publikacji:
    1994-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    05.30.Jp
    71.28.+d
    Opis:
    We discuss a few models developed for description of superconductivity with very short coherence length and point out their formal equivalence to specific spin models, such as an anisotropic Heisenberg model (s = 1/2) with two- and four-spin exchange coupling and with fixed magnetization in the z-direction, an XY-Z model with single ion anisotropy and a Kondo-lattice model with anisotropic on-site exchange. New results concerning the phase diagram of the Hubbard model with strong attraction, the electromagnetic properties of systems with the first order superconducting transition and a possibility of local charge moment compensation in systems of coexisting bound pairs and itinerant electrons are presented.
    Źródło:
    Acta Physica Polonica A; 1994, 85, 1; 117-131
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground State Phase Diagrams of the Extended Hubbard Model with Repulsive Pair-Hopping Interaction for Nonfrustrated 2D Lattice
    Autorzy:
    Czart, W.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1385232.pdf
    Data publikacji:
    2015-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    74.20.Mn
    Opis:
    We analyze the extended Hubbard model with pair-hopping interaction J, i.e. the Penson-Kolb-Hubbard model, in the case of repulsive J (J < 0) within the (broken symmetry) Hartree-Fock approximation. We focus our study on the effects of on-site U interaction on the mutual stability of magnetic, charge-ordered, and superconducting states including the eta-pairing phase, i.e. the state with the Cooper-pair center-of-mass momentum q=Q. The ground state phase diagrams are obtained for arbitrary particle concentration n on nonfrustrated d=2 square lattice.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 2; 275-277
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ground State Phase Properties of the Penson-Kolb-Hubbard Model with Attractive Pair-Hopping Interaction
    Autorzy:
    Czart, W.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1385235.pdf
    Data publikacji:
    2015-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    74.20.Mn
    Opis:
    We study the ground state phase diagrams of the extended Hubbard model with the pair-hopping interaction J, i.e. the Penson-Kolb-Hubbard model. We concentrate on the case of attractive J (J > 0) which can stabilise s-wave pairing superconductivity in the system and competes with the on-site repulsive U. The evolution of the phase diagrams and order parameters for arbitrary electron density and representative values of the interaction parameters are analyzed within the (broken symmetry) Hartree-Fock approximation. The calculations are performed for the case of nearest-neighbors electron hopping t on the d=2 square lattice.
    Źródło:
    Acta Physica Polonica A; 2015, 127, 2; 278-280
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Quest for Band Renormalization and Self-Energy in Correlated f-Electron Systems
    Autorzy:
    Durakiewicz, T.
    Riseborough, P.
    Batista, C.
    Yang, Y.
    Oppeneer, P.
    Joyce, J.
    Bauer, E.
    Graham, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1538778.pdf
    Data publikacji:
    2010-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    79.60.-i
    71.28.+d
    74.25.Jb
    Opis:
    Coexisting low-energy scales are observed in f-electron materials. The information about some of low-energy scales is imprinted in the electron self-energy, which can be measured by angle-resolved photoemission (ARPES). Such measurements in d-electron materials over the last decade were based on high energy- and momentum- resolution ARPES techniques used to extract the self-energy information from measured spectra. Simultaneously, many-body theoretical approaches have been developed to find a link between the self-energy and many-body interactions. Here we show the transcription of such methods from d-electrons to f-electrons by presenting the first example of low energy scales in the f-electron material $USb_2$, measured with synchrotron-based ARPES. The proposed approach will help in answering the fundamental questions about the complex nature of the heavy fermion state.
    Źródło:
    Acta Physica Polonica A; 2010, 117, 2; 264-267
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Phase Diagrams of the Penson-Kolb-Hubbard Model with Repulsive Pair-Hopping Interaction
    Autorzy:
    Czart, W.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1398641.pdf
    Data publikacji:
    2016-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    74.20.Mn
    Opis:
    We study the extended Hubbard model with on-site density-density U and intersite pair hopping J interactions, i.e. the Penson-Kolb-Hubbard model. This report focuses mainly on the properties of the model at T ≥q 0 in the case of repulsive J (J < 0) which may stabilize superconductivity with η-pairing. The analysis is performed within the (broken symmetry) Hartree-Fock approximation for arbitrary interaction parameters (J < 0 and U) and electron concentration (0 < n < 2) on the d = 2 square lattice. The phase diagrams of the model at T=0 and at finite temperatures are examined taking into account magnetic and charge-ordered phases and superconducting states with η- and s-wave pairing.
    Źródło:
    Acta Physica Polonica A; 2016, 130, 2; 613-616
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Tunneling Spectroscopy Studies of $SmB_6$ and $YbB_{12}$
    Autorzy:
    Baťková, M.
    Baťko, I.
    Konovalova, E.
    Shitsevalova, N.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813633.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    75.30.Mb
    73.40.Gk
    Opis:
    Reported electron tunneling studies of $SmB_6$ and $YbB_{12}$ in the temperature region with a strongly temperature activated transport reveal a qualitative change of tunneling regime upon cooling. While the differential conductance curves above 50 K resemble the tunneling between two different metals, the spectra observed at 4.2 K are typical of the tunneling between a metal and a (narrow-gap) valence fluctuating semiconductor.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 255-258
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Universal Scaling of Basic Properties of the Heavy-Fermion Superconductors
    Autorzy:
    Karbowski, J.
    Spałek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1930572.pdf
    Data publikacji:
    1994-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.70.Tx
    75.30.Mb
    71.28.+d
    Opis:
    We show that the properties of the heavy-electron superconducting state induced by the interorbital kinetic exchange scale with the effective mass renormalization m*/m$\text{}_{0}$ ~ 1/T$\text{}_{K}$. Explicitly, the pairing potential J̃ ~ J(m$\text{}_{0}$/m*)ln$\text{}^{2}$(m$\text{}_{0}$/m*), where J is the magnitude of the bare Kondo coupling; the coherence length ξ ~ T$\text{}_{K}$/T$\text{}_{c}$ where T$\text{}_{c}$ is the transition temperature, whereas the penetration depth λ ~ (m*/m$\text{}_{0}$)$\text{}^{½}$ so that λ/ξ >> 1. We also determine the scaling of magnetic critical fields.
    Źródło:
    Acta Physica Polonica A; 1994, 85, 2; 341-345
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Exchange Interaction as a Source of Real Space Pairing in High Temperature Superconductors and Heavy Fermions: a Brief Overview
    Autorzy:
    Spałek, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1860823.pdf
    Data publikacji:
    1994-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    75.10.Lp
    74.70.Vy
    Opis:
    We characterize the principal difference between the pairing induced by the kinetic exchange interactions for the Fermi-liquid and spin-liquid phases. In the case of hybridized electrons the Kondo-exchange induced pairing is invoked, whereas for a single narrow-band case kinetic exchange is responsible for the spin singlet pairing. The former interaction is applied to heavy-fermion systems, whereas the latter is employed to the high temperature superconductors. The current situation concerning the applicability of our theoretical models is briefly and critically assessed.
    Źródło:
    Acta Physica Polonica A; 1994, 85, 1; 39-52
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Raman Spectroscopy of Multiphonon Emission Process in Ni-Doped PbTe
    Autorzy:
    Romčević, N.
    Trajić, J.
    Hadžić, B.
    Romčević, M.
    Stojanović, D.
    Lazarević, Z.
    Kuznetsova, T.
    Khokhlov, D.
    Rudolf, R.
    Anžel, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1807841.pdf
    Data publikacji:
    2009-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    63.20.-e
    78.30.-j
    Opis:
    In this paper, we present room temperature unpolarized Raman scattering spectra of Ni doped PbTe single crystal sample. Crystal of PbTe(Ni) was grown by the Bridgman method. The Ni concentration in the sample used here was 1× $10^{19}$ at./$cm^{3}$. Well resolved peaks appear at about 126, 143, 181, 362 and 724 $cm^{-1}$. The modes at 126 and 143 $cm^{-1}$, which are also observed in other telluride compounds, originate from vibrations in $TeO_2$. We assume that the mode at about 181 $cm^{-1}$ is connected to excitations of a local phonon mode in the vicinity of an impurity atom (donor $Ni^{3+}$ state). Modes at about 362 $cm^{-1}$ and 724 $cm^{-1}$ are the second and fourth harmonic of a local phonon mode, registered here due to multiphonon emission.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 1; 91-92
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superfluid Characteristics of Induced-Pairing Model
    Autorzy:
    Czart, W. R.
    Szkudlarek, M.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/1955834.pdf
    Data publikacji:
    1997-02
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.28.+d
    74.25.Ha
    74.20.-z
    Opis:
    We study the electromagnetic and thermodynamic properties of a model of coexisting local electron pairs and itinerant carriers coupled via the intersubsystem charge exchange. The calculations of the London penetration depth, the energy gap, the magnetic critical fields and the coherence length in the superconducting phase are performed. The effects of reduced binding energy of local pairs are discussed.
    Źródło:
    Acta Physica Polonica A; 1997, 91, 2; 415-418
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconducting Characteristics of the Penson-Kolb Model
    Autorzy:
    Czart, W. R.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2012898.pdf
    Data publikacji:
    2000-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    74.25.Ha
    Opis:
    We study superconducting properties of the Penson-Kolb model, i.e. the tight-binding model with the pair-hopping (intersite charge exchange) interaction J. The evolution of the critical fields, the coherence length, the Ginzburg ratio, and the London penetration depth with particle concentration n and pairing strength are determined. The results are compared with those found earlier for the attractive Hubbard model.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 1; 217-220
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconducting Properties of theη-Pairing State in the Penson-Kolb-Hubbard Model
    Autorzy:
    Czart, W. R.
    Robaszkiewicz, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2041460.pdf
    Data publikacji:
    2004-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    71.28.+d
    74.25.Ha
    Opis:
    The Penson-Kolb-Hubbard model, i.e. the Hubbard model with the pair-hopping interaction J is studied. We focus on the properties of the superconducting state with the Cooper-pair center-of-mass momentum q= Q (η-phase). The transition into theη-phase, which is favorized by the repulsive J (J<0) is found to occur only above some critical value |J$\text{}_{c}$|, dependent on band filling, on-site interaction U and band structure, and the system never exhibits standard BCS-like features. This is in obvious contrast with the properties of the isotropic s-wave state, stabilized by the attractive J and attractive U, which exhibit at T=0 a smooth crossover from the BCS-like limit to that of tightly bound pairs with increasing pairing strength.
    Źródło:
    Acta Physica Polonica A; 2004, 106, 5; 709-713
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconductivity, Charge Orderings and Phase Separations in Systems with Local Electron Pairing
    Autorzy:
    Robaszkiewicz, S.
    Pawłowski, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1946347.pdf
    Data publikacji:
    1996-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    05.30.Jp
    71.28.+d
    Opis:
    We study two effective models developed for description of superconductors with short-coherence length: (i) the extended Hubbard model with on-site attraction and intersite repulsion, (ii) the model of hard-core charged bosons on a lattice. The analysis is concentrated on the problem of phase separations and competition between superconductivity (SS) and charge-density-wave (CDW) orderings. The phase diagrams of the systems are shown to consist of at least seven different states, including 3 types of phase separated (PS) states: CDW-SS (PS1), CDW-normal (PS2) and the state of electron droplets (PS3). By taking into account the PS states and the effects of longer-range density-density interactions (beyond nearest neighbors) our paper substantially generalizes and modifies the conclusions of previous papers concerning the models considered.
    Źródło:
    Acta Physica Polonica A; 1996, 90, 3; 569-586
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Influence of Lattice Defects on the Ground-State Properties of the Falicov-Kimball Model in Two Dimensions
    Autorzy:
    Žonda, M.
    Farkašovský, P.
    Čenčariková, H.
    Powiązania:
    https://bibliotekanauki.pl/articles/1813656.pdf
    Data publikacji:
    2008-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.10.Lp
    71.27.+a
    71.28.+d
    71.30.+h
    Opis:
    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 $Sm_{1-x}B_6$.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 1; 291-294
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Features of Energy Spectrum of Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te Doped with V
    Autorzy:
    Artamkin, A. I.
    Dobrovolsky, A. A.
    Dziawa, P.
    Story, T.
    Slynko, E. I.
    Slynko, V. E.
    Ryabova, L. I.
    Khokhlov, D. R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2046904.pdf
    Data publikacji:
    2006-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.20.Nr
    71.28.+d
    71.55.-i
    72.40.+w
    Opis:
    Recently new effects that are not characteristic of undoped lead telluride, such as the Fermi level pinning, giant negative magnetoresistance, were observed in Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te alloys doped with transition and rare earth elements - Cr, Mo, Yb. We have studied transport and magnetic properties of Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te doped with another transition element - vanadium. A series of Pb$\text{}_{1-x}$Mn$\text{}_{x}$Te(V) samples of different composition and degree of doping was investigated. It was observed that the resistivity demonstrates activation behavior at low temperatures for the samples with considerable amount of vanadium as well as for the samples without vanadium. The activation energy is proportional to the Mn content. In some of the samples, photoconductivity was observed at low temperatures. The results are discussed in terms of a model assuming formation of the impurity level by the vanadium impurity and the effect of the Fermi level pinning by this level.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 2; 151-156
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Influence of Yttrium Substitution οn the Electronic Structure and Magnetic Moment οf $Gd_{7-x}Y_{x}Pd_{3}$ (x = 0, 1, 2, 3, 4)
    Autorzy:
    Klimczak, M.
    Talik, E.
    Tran, V.
    Powiązania:
    https://bibliotekanauki.pl/articles/1810460.pdf
    Data publikacji:
    2009-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.20.Lp
    71.28.+d
    75.40.Cx
    75.60.Ej
    Opis:
    The electronic structure and magnetic properties of $Gd_{7-x}Y_{x}Pd_{3}$ (x = 0, 1, 2, 4) single crystals were examined. These compounds crystallized in the same crystal structure type $(Th_{7}Fe_{3})$ with the same c/a ratio of 0.63. A strongly anisotropic behavior of the magnetic and transport properties was found. Magnetic frustration and spin fluctuations on the palladium atoms are responsible for the complex magnetic properties of this ternary compound. As a part of current research we presented further characteristic of the $Gd_{7-x}Y_{x}Pd_{3}$ (x = 0, 1, 2, 4) single crystal.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 1; 200-202
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pressure Induced Transitions in Heavy-Fermion Systems footnotemark
    Autorzy:
    Zhang, Sun
    Dong, Yi-Qiao
    Powiązania:
    https://bibliotekanauki.pl/articles/1401900.pdf
    Data publikacji:
    2015-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.30.Mb
    75.20.Hr
    71.28.+d
    74.62.Fj
    Opis:
    In this paper, the electron-type heavy-fermion system and the hole-type heavy-fermion system are classified by means of the cell-volume difference between two typical valence states of f ions. Two kinds of transitions induced by pressure are studied theoretically within a unified picture presented for both two types of heavy-fermion systems. Among these transitions, the incoherence-to-coherence transition in the electron-type heavy-fermion system is confirmed intensively in experiments, while the coherence-to-incoherence transition in the hole-type heavy-fermion system is discussed as a prediction for further observations.
    Źródło:
    Acta Physica Polonica A; 2015, 128, 3; 389-393
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Influence of Coulomb Interactions on the Properties of Induced Pairing Model
    Autorzy:
    Czart, W. R.
    Robaszkiewicz, St.
    Powiązania:
    https://bibliotekanauki.pl/articles/2027440.pdf
    Data publikacji:
    2001-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.20.-z
    74.20.Mn
    71.28.+d
    74.25.Ha
    Opis:
    We study the superconducting properties of a model of coexisting itinerant carriers and local pairs with finite binding energy, taking into account the effects of Coulomb (density-density) and direct pair hopping interactions. The evolution of the phase diagrams and superfluid characteristics with electron concentration, interaction parameters and the relative position of the bands is examined. The model is found to exhibit several kinds of superconducting behaviors ranging from the BCS-like to the local-pair-like. The relevance of the obtained results to the interpretation of experimental data for the doped bismuthates (Ba$\text{}_{1-x}$K$\text{}_{x}$BiO$\text{}_{3}$ and BaPb$\text{}_{1-x}$BiO$\text{}_{3}$) is pointed out.
    Źródło:
    Acta Physica Polonica A; 2001, 100, 1; 75-88
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Electronic Correlations within Fermionic Lattice Models
    Autorzy:
    Matlak, M.
    Grabiec, B.
    Krawiec, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2047738.pdf
    Data publikacji:
    2007-09
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.10.-w
    71.10.Ca
    71.10.Fd
    71.20.Be
    71.27.+a
    71.28.+d
    73.21.La
    78.67.Bf
    Opis:
    We investigate two-site electronic correlations within generalized Hubbard model, which incorporates the conventional Hubbard model (parameters: t (hopping between nearest neighbours), U (Coulomb repulsion (attraction))) supplemented by the intersite Coulomb interactions (parameters: J$\text{}^{(1)}$ (parallel spins), J$\text{}^{(2)}$ (antiparallel spins)) and the hopping of the intrasite Cooper pairs (parameter: V). As a first step we find the eigenvalues E$\text{}_{α}$ and eigenvectors |E$\text{}_{α}$〉 of the dimer and we represent each partial Hamiltonian E$\text{}_{α}$|E $\text{}_{α}$〉〈 E$\text{}_{α}$| (α=1,2,...,16) in the second quantization with the use of the Hubbard and spin operators. Each dimer energy level possesses its own Hamiltonian describing different two-site interactions which can be active only in the case when the level will be occupied by the electrons. A typical feature is the appearance of two generalized t-J interactions ascribed to two different energy levels which do not vanish even for U=J$\text{}^{(1)}$=J{(2)}=V=0 and their coupling constants are equal to ±t in this case. In the large linebreak U-limit for J$\text{}^{(1)}$=J$\text{}^{(2)}$=V=0 there is only one t-J interaction with coupling constant equal to 4t$\text{}^{2}$/|U| as in the case of a real lattice. The competition between ferromagnetism, antiferromagnetism and superconductivity (intrasite and intersite pairings) is also a typical feature of the model because it persists in the case U=J$\text{}^{(1)}$=J$\text{}^{(2)}$=V=0 and t≢0. The same types of the electronic, competitive interactions are scattered between different energy levels and therefore their thermodynamical activities are dependent on the occupation of these levels. It qualitatively explains the origin of the phase diagram of the model. We consider also a real lattice as a set of interacting dimers to show that the competition between magnetism and superconductivity seems to be universal for fermionic lattice models.
    Źródło:
    Acta Physica Polonica A; 2007, 112, 3; 537-547
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
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