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Tytuł:
Indirect RKKY-Type Interaction by Direct Oxygen Hopping
Autorzy:
Rodriguez-Nuńez, J.
Coqblin, B.
Beck, H.
Konior, J.
Powiązania:
https://bibliotekanauki.pl/articles/1930566.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Mn
74.25.Jb
Opis:
The three-band Emery model, describing the holes in the CuO$\text{}_{2}$ planes of the high-temperature superconducting oxides, is considered. The model includes the direct oxygen-oxygen hopping integral t$\text{}_{pp}$. The exact Bogolyubov transformation is used to exclude one oxygen band and obtain a two-dimensional Anderson model. Afterward, the effective Hamiltonian is obtained by eliminating the second oxygen band with the use of two approximate canonical transformations. The effective Hamiltonian describes the spins residing on the copper sites and interacting through an indirect interaction J$\text{}_{SX}$(R), where R is the distance between two copper ions. J$\text{}_{SX}$(R) depends on the doping rate δ and is a decaying function of R. Numerical results for J$\text{}_{SX}$(R) are given for different doping rates δ for the case of parabolic bands. The obtained interaction J$\text{}_{SX}$(R), when added to the original antiferromagnetic interaction (present in oxides at δ = 0), might lead to a frustration of the long-range antiferromagnetic ordering upon doping.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 317-322
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electronic Properties of CeNiAl₄ Based on ab initio Calculations and XPS Measurements
Autorzy:
Werwiński, M.
Chełkowska, G.
Szajek, A.
Kowalczyk, A.
Powiązania:
https://bibliotekanauki.pl/articles/1030430.pdf
Data publikacji:
2018-03
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.20.b
74.25.Jb
Opis:
The CeNiAl₄ compound crystallizes in an orthorhombic YNiAl₄-type structure with a Cmcm space group. The earlier susceptibility data and X-ray photoelectron spectroscopy (XPS) suggested a localized character of the 4f states in CeNiAl₄ with a valence state close to a Ce⁺³ ion. In this work we present a combined theoretical and experimental study of the electronic structure for the Kondo dense system CeNiAl₄ based on the XPS data and ab initio calculations. Using the band structure calculations the theoretical XPS valence band spectra are evaluated. Below the Fermi energy the total density of states contains mainly 3d states of Ni hybridized with Ce 4f states.
Źródło:
Acta Physica Polonica A; 2018, 133, 3; 517-519
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Simple Band Model of Doped Fullerene Crystal
Autorzy:
Koper, A.
Mucha, M.
Powiązania:
https://bibliotekanauki.pl/articles/2012907.pdf
Data publikacji:
2000-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Mn
74.25.Kc
74.25.Jb
Opis:
We use quantum billiard with many scattering centers to describe conducting electrons properties in A$\text{}_{n}$C$\text{}_{60}$ crystals, where A denotes alkali metal. We focus our attention on the A$\text{}_{3}$C$\text{}_{60}$ crystal, for which we calculate the band structure, density of states, and conductivity for normal electrons. Conductivity shows linear dependence on temperature in this model, which agrees well with experimental data. We also discuss consequences of our results for superconductivity mechanism in A$\text{}_{3}$C$\text{}_{60}$ and possibilities of analogous approach to describe electron properties in fused fullerenes and multiply connected carbon clusters.
Źródło:
Acta Physica Polonica A; 2000, 97, 1; 233-236
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Pseudogap Phenomenon in High-T$\text{}_{c}$ Superconductors
Autorzy:
Ranninger, J.
Romano, A.
Powiązania:
https://bibliotekanauki.pl/articles/2011238.pdf
Data publikacji:
2000-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.25.-q
74.25.Jb
Opis:
We review the possible mechanisms leading up to the phenomenon of a pseudogap which characterizes the normal-state properties of high-T$\text{}_{c}$ superconductors. We suggest that this pseudogap is not due to superconducting phase fluctuations and hence is not related to a crossover between a BCS state of Cooper pairs and a Bose-Einstein condensation of local pairs. We rather argue that it is due to uncorrelated pairing which is already manifest in the local electronic structure and accessible by photoemission and tunneling experiments.
Źródło:
Acta Physica Polonica A; 2000, 97, 1; 157-164
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Superconductivity, Weak Itinerant Ferromagnetism and Electronic Band Structure of Y$\text{}_{9}$Co$\text{}_{7}$
Autorzy:
Kołodziejczyk, A.
Wiendlocha, B.
Zalecki, R.
Toboła, J.
Kaprzyk, S.
Powiązania:
https://bibliotekanauki.pl/articles/2047310.pdf
Data publikacji:
2007-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.25.Jb
74.25.Ha
74.20.Mn
Opis:
The paper presents experimental results for the intermetallic compound Y$\text{}_{9}$Co$\text{}_{7}$ which is the first very weak itinerant ferromagnetic superconductor. The measurements of electrical resistivity, susceptibility, magnetization, specific heat, nuclear magnetic resonance, and other properties show the magnetic transition at T$\text{}_{C}$≈ 4.5 K and the onset of superconductivity at about T$\text{}_{S}$≈ 2.5 K, revealing the coexistence state within a temperature interval below T$\text{}_{S}$. A few of the results are shortly reviewed and discussed. We focus attention on our recent ultraviolet photoemission spectroscopy and their comparison with our band structure calculations. Interpretations are considered which take into account the characteristic structure of the compound and different possible types of magnetic ordering.
Źródło:
Acta Physica Polonica A; 2007, 111, 4; 513-526
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Calculation of Optical and Spin-Hamiltonian Parameters for $Mn^{4+}$ Doped in $LiGa_{5}O_{8}$
Autorzy:
Ciresan, M.
Stanciu, M.
Avram, N.
Powiązania:
https://bibliotekanauki.pl/articles/1791234.pdf
Data publikacji:
2009-10
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.25.Jb
74.25.nd
76.30.-v
Opis:
The aim of this paper is to investigate, from theoretical point of view, the optical spectra and EPR (g-factors) parameters for $Mn^{4+}:LiGa_{5}O_{8}$. The optical energy levels scheme has been obtained by the diagonalization of the Hamiltonian of the system, using all 50 wave functions of the LS terms of $3d^{3}$ electron configuration. The crystal field parameters have been obtained in the exchange charge model of crystal field, taking into account the structure of the host matrix and effects of the covalent bond formation between the $Mn^{4+}$ with $O^{2-}$. The satisfactory agreement with experimental data is obtained.
Źródło:
Acta Physica Polonica A; 2009, 116, 4; 547-549
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electronic Structure and Fermiology of High-T$\text{}_{c}$ Superconductors
Autorzy:
Bansil, A.
Kaprzyk, S.
Powiązania:
https://bibliotekanauki.pl/articles/1929378.pdf
Data publikacji:
1993-07
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.25.-s
74.20.Mn
74.25.Jb
Opis:
We briefly discuss some of our recent results in three areas, all related to issues concerning the electronic structure and fermiology of the high-T$\text{}_{c}$'s. (i) First-principles band theory based computations of the electron-positron momentum density relevant for the interpretation of the positron annihilation (2D-ACAR) experiments; results for YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ are discussed. (ii) Another k-resolved spectroscopy where such first-principles comparisons between the computed and measured spectral intensities have been crucially important is the angle-resolved photoemission experiment; we discuss results for the (001)-surface of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ where computations yield considerable insight into the nature and origin of the spectral signal associated with the CuO$\text{}_{2}$ plane bands. (iii) The study of effects of substitutions and of oxygen-vacancy disorder in the high-T$\text{}_{c}$'s; here results for the LaSrCuO$\text{}_{4}$, and Ba-K-Bi-O and Ba-Pb-Bi-O systems, with focus on the nature of the van Hove singularity in the vicinity of the Fermi energy are presented.
Źródło:
Acta Physica Polonica A; 1993, 84, 1; 7-20
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Effect of van Hove Singularity on T$\text{}_{c}$ in Rb doped C$\text{}_{60}$
Autorzy:
Agrawal, B. K.
Agrawal, S.
Yadav, P. S.
Srivastava, P.
Srivastava, R.
Singh, S.
Powiązania:
https://bibliotekanauki.pl/articles/2035748.pdf
Data publikacji:
2003-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.25.Jb
74.62.Fj
74.70.Wz
Opis:
In the present study we investigate the role of van Hove singularity on the optimization of T$\text{}_{c}$ in Rb doped fullerenes C$\text{}_{60}$ Rb$\text{}_{3}$. A first principles self-consistent full potential linear muffin-tin orbital method using density functional theory in local density approximation was employed. The doped Rb atoms are of two types occupying the tetrahedral and interstitial positions in the fcc lattice. The added Rb atoms fill the t$\text{}_{1u}$ band of the undoped fullerenes C$\text{}_{60}$ up to half which makes C$\text{}_{60}$Rb$\text{}_{3}$ conducting. Saddle points leading to van Hove singularities are observed in the neighbourhood of the symmetry point L. The shifting of the van Hove singularity with the volume of the lattice is investigated. We observe a saddle point just at the Fermi level for a lattice constant of 14.435Å. The highest value of T$\text{}_{c}$ should thus be observed at the above lattice constant. This result is in excellent agreement with the observed high value of T$\text{}_{c}$ measured in C$\text{}_{60}$Rb$\text{}_{3}$ for a lattice constant of 14.435Å.
Źródło:
Acta Physica Polonica A; 2003, 103, 5; 477-482
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Quasiparticle Interference in a Superconducting State with a Fourfold Phase Change
Autorzy:
Pisarski, P.
Harań, G.
Powiązania:
https://bibliotekanauki.pl/articles/2047342.pdf
Data publikacji:
2007-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Rp
74.25.Jb
74.62.Dh
Opis:
Quantum interference revealed in Bi$\text{}_{2}$Sr$\text{}_{2}$Ca Cu$\text{}_{2}$O$\text{}_{8+δ}$ by Fourier transform scanning spectroscopy is primarily determined by maxima of the joint density of states which correspond to an octet of scattering wave vectors connecting points at the constant quasiparticle energy contours where the density of states is maximal. We consider a superconductor with a constant quasiparticle density of states where the interference is due to the fourfold change in the phase of the order parameter. Our results may be helpful in a discussion of the interference in a d-wave superconductor at the tunneling energy exceeding the gap magnitude.
Źródło:
Acta Physica Polonica A; 2007, 111, 5; 791-794
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Bismuth Valence in a $Tl_{0.7}Bi_{0.3}Sr_{1.6}Ba_{0.4}CaCu_{2}O_{y}$ Superconductor from X-Ray Photoemission Spectroscopy
Autorzy:
Zalecki, R.
Woch, W.
Kowalik, M.
Kołodziejczyk, A.
Gritzner, G.
Powiązania:
https://bibliotekanauki.pl/articles/1537186.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.72.-h
74.25.Jb
79.60.-i
Opis:
The X-ray electron photoemission spectra of a $Tl_{0.7}Bi_{0.3}Sr_{1.6}Ba_{0.4}CaCu_2O_{y}$ superconductor were measured with $Al K_{α}$ and $Mg K_{α}$ radiation at room temperature. The Bi 4f spectrum was compared to the same spectra of $Bi_{1.75}Pb_{0.35}Sr_{1.9}Ca_{2.05}Cu_{3.05}O_{y}$ and $Tl_{0.6}Pb_{0.4}Sr_{1.6}Ba_{0.4}Ca_2Cu_3O_{y}$ superconductors. In Bi,Pb-based superconductor only one type of $Bi^{3+}$ ions is present. The Bi 4f spectrum in the Tl,Bi-superconductor consists of two contributions due to the different valences. The component from $Bi^{5+}$ lines is in higher binding energy than from $Bi^{3+}$. The ratio of trivalent $Bi^{3+}$ to pentavalent $Bi^{5+}$ bismuth ions was calculated from decomposition of the spin-orbit split spectrum of the Bi 4f photoelectrons. The conclusion is that Bi is present in trivalent and in pentavalent form and the ratio of $Bi^{3+}$ to $Bi^{5+}$ is 1.87 ± 0.02.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 393-395
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Cooper Pair in Two Nonstandard Situations
Autorzy:
Wróbel, P.
Starypan, Z.
Kaczmarczyk, J.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/2046740.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.25.Jb
71.10.-w
Opis:
We summarize briefly our recent work on the bound states of two electrons (Cooper pairs) in two nonstandard situations: when the quasiparticle masses depend on spin and when an electron pair is localized on a two-dimensional quantum dot and placed in an applied magnetic field. In both cases we are dealing with an extension of the original Cooper approach. The applicability of the results is briefly mentioned.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 541-548
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Improved Transresistance Characteristics of Inductance-gate Type SFFT Using AFM Lithography
Autorzy:
Ko, S.
Powiązania:
https://bibliotekanauki.pl/articles/1400571.pdf
Data publikacji:
2015-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Pq
74.25.F-
74.25.Jb
74.55.+V
Opis:
An atomic force microscope (AFM) was used to locally anodize the serial channels of an inductance-gate type superconducting flux flow transistor (SFFT) as narrow slits with a width of 50 μm, a space of 25 μm, and 12 turns, to improve the transresistance value. Among the serial channels that were anodized with the scanning tip of the AFM in the drain current line, channels 1 and 2 were 7.3 and 7.9 μm wide, and 531 and 461 nm high, respectively. The critical current density in the serial channel of the fabricated SFFT, which was determined using an AFM modification method, was decreased by increasing the gate current. The measured current-voltage curves were compared with the simulated ones. The maximum transresistance value was 0.56 Ω at the drain current of 20 mA when the gate current was 6 mA. The transresistance characteristics of the inductance-gate type SFFT could be more improved than that of the single-channel type SFFT using an inductively coupled plasma lithography method
Źródło:
Acta Physica Polonica A; 2015, 127, 4; 928-930
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Mixed Valence Quasiparticles in CuO$\text{}_{2}$ Planes
Autorzy:
Bała, J.
Oleś, A. M.
Powiązania:
https://bibliotekanauki.pl/articles/1955491.pdf
Data publikacji:
1997-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.25.Jb
75.30.Ds
75.10.Lp
Opis:
The motion of a single hole doped to a CuO$\text{}_{2}$ plane of a high temperature superconductor is described by a spin-fermion model which treats explicitly the hybridization with the upper Hubbard band. One finds that sectors of Zhang-Rice bound states coexist with reasonably damped oxygen and copper-like quasiparticles, with a considerable transfer of the spectral weight to the upper Hubbard band. The oxygen states have small dispersions and can be identified in the angle-resolved photoemission experiments for Bi$\text{}_{2}$Sr$\text{}_{2}$CaCu$\text{}_{2}$O$\text{}_{8}$.
Źródło:
Acta Physica Polonica A; 1997, 91, 2; 333-336
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Resonant Photoemission Spectroscopy Study on the Contribution of the Yb 4f States to the Electronic Structure of ZnO
Autorzy:
Demchenko, I.
Melikhov, Y.
Konstantynov, P.
Ratajczak, R.
Barcz, A.
Guziewicz, E.
Powiązania:
https://bibliotekanauki.pl/articles/1030972.pdf
Data publikacji:
2018-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
77.55.hf
74.25.Jb
33.60.+q
Opis:
The electronic structure of Yb implanted ZnO has been studied by the resonant photoemission spectroscopy. The contribution of the Yb 4f partial density of states is predominant at binding energy about 7.5 and ≈11.7 eV below the VB maximum. At photon energy about 182 eV the multiplet structure around 11.7 eV shows the strongest resonance that corresponds to the ¹I multiplet which is almost exclusively responsible for this resonance, while ³H and ³F states are responsible for the resonance around 7.5 eV. It was also found that the Yb 4f partial density of states distribution shows some similarity to Yb₂O₃.
Źródło:
Acta Physica Polonica A; 2018, 133, 4; 907-909
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Many-Body Effects Observed in the Positron Annihilation Experiment
Autorzy:
Kontrym-Sznajd, G.
Sormann, H.
Powiązania:
https://bibliotekanauki.pl/articles/2042161.pdf
Data publikacji:
2005-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
78.70.Ck
74.25.Jb
Opis:
This paper is devoted to study many-body effects in the positron annihilation experiment, both electron-positron (e-p) and electron-electron (e-e) correlations. Various theories of the e-p interaction in real solids were used to verify them by comparing theoretical and experimental e-p momentum densities in Cu and Y. We show that the lattice potential has an essential influence on the e-p correlation effects, i.e. their proper description must be done via periodic lattice potential as e.g. in the Bloch modified ladder theory. Moreover, it is not true that the dynamic parts of the direct e-p and e-e interactions cancel each other because e-e correlations are observed not only in the Compton scattering but also in the positron annihilation experiments.
Źródło:
Acta Physica Polonica A; 2005, 107, 4; 562-569
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 19

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