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Wyświetlanie 1-15 z 89
Tytuł:
Vortex Properties in a Model with Local Pairs
Autorzy:
Śledź, Ż.
Mierzejewski, M.
Maśka, M. M.
Powiązania:
https://bibliotekanauki.pl/articles/2046800.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.25.Ha
74.20.-z
Opis:
We investigate the vortex structure in the Penson-Kolb model with and without impurities. We focus on the consequences arising from the non-local field-dependent pairing interaction for the vortex profile, current distribution, and the local density of states.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 653-656
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Unconventional Superconducting States of an Almost Localized Fermionic Liquid with Nonstandard Quasiparticles: Generalized Gutzwiller Approach
Autorzy:
Kaczmarczyk, J.
Jędrak, J.
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1536614.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
71.27.+a
71.10.Ca
Opis:
We apply the concept of generalized (almost localized) Fermi liquid and associated with it unconventional superconductivity with Cooper pairs composed of quasiparticles with the spin dependent masses (in an applied field) and with the effective field, both induced by electron correlations. The pairing among quasiparticles takes place either in reciprocal space (Sect. 2) or in real space (Sect. 3) and is induced by the kinetic exchange of either superexchange (in the generic narrow-band situation) or Kondo-type interaction (in the Kondo-lattice limit of the periodic Anderson model). While the main features of this type of Fermi liquid have been introduced earlier, we present here a picture which is applicable to both heavy-fermion and high-$T_{c}$ superconductivity within a single narrow-band representation of correlated states. Our approach introduces a set of additional concepts (spin-dependent masses, effective fields induced by electron correlations), for which the Landau concept of the Fermi liquid represents still a workable scheme. In the limit of the Kondo lattice, we present the phase diagram incorporating the Fulde-Ferrell-Larkin-Ovchinnikov phase within the BCS-type of pairing, whereas in that of the t-J model we show that the proper choice of renormalization factors and constraints is crucial for the mean-field description of the superconducting state.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 261-266
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Topological Criticality on Brink of the Mott Transition in High-T$\text{}_{c}$ Superconductors
Autorzy:
Kopeć, T. K.
Powiązania:
https://bibliotekanauki.pl/articles/2046733.pdf
Data publikacji:
2006-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.20.Fg
71.10.Pm
Opis:
The concept of topological excitations and the related ground state degeneracy are employed to establish an effective theory of the superconducting state evolving from the Mott insulator for high-T$\text{}_{c}$ cuprates. The theory includes the effects of the relevant energy scales with the emphasis on the Coulomb interaction $U$ governed by the electromagnetic U(1) compact group. The results are obtained for the layered t-t'-t$\text{}_{⊥}$-U-J system of strongly correlated electrons relevant for cuprates. Casting the Coulomb interaction in terms of composite-fermions via the gauge flux attachment facility, we show that instanton events in the Matsubara "imaginary time", labelled by a topological winding numbers, governed by gauge flux changes by an integer multiple of 2π, are essential configurations of the phase field dual to the charge. The impact of these topological excitations is calculated for the phase diagram, which displays the "hidden" quantum critical point on verge of the Mott transition that is given by a divergence of the charge compressibility.
Źródło:
Acta Physica Polonica A; 2006, 109, 4-5; 499-506
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Thermodynamic Properties of D-Wave Paired Superconductors in the Low Temperature and Subcritical Regions
Autorzy:
Kumala, W.
Gonczarek, R.
Mulak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2013257.pdf
Data publikacji:
2000-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
Opis:
D-wave paired isotropic Fermi system in the limiting cases T → T$\text{}_{c}$ and T → 0 is considered. Values of the energy gap, the thermodynamic potential, and the specific heat as a function of temperature are given for admissible solutions and compared with values for S-wave paired system. It is shown that the linear term of low temperature specific heat vanishes likewise in case of S-wave pairing. The obtained results make prospects to define the geometry of the energy gap in virtue of the behavior of the specific heat in the limiting temperature cases for heavy-fermion superconductors.
Źródło:
Acta Physica Polonica A; 2000, 97, 4; 693-703
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Thermodynamic Properties of D-Wave Paired Superconductors
Autorzy:
Gonczarek, R.
Mulak, M.
Kumala, W.
Powiązania:
https://bibliotekanauki.pl/articles/1994689.pdf
Data publikacji:
1999-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
Opis:
The D-wave paired Fermi system is considered in the frame of generalized gap equation obtained in a BCS-like approach. It is shown that the thermodynamic functions of a system, as the thermodynamic potential, entropy and heat capacity differences between the normal and superconducting state are precisely defined functionals of the energy gap as a function of temperature. The derived formulas are identical as those obtained for S-wave paired Fermi system. It states that the developed formalism can be applied, in practice, to investigation of real superconductors in which a singlet state is realized. Some numerical results illustrating prospects and capabilities of the presented formalism are given for chosen structures of the order parameter.
Źródło:
Acta Physica Polonica A; 1999, 95, 2; 231-242
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theory of Unconventional Superconductivity in Strongly Correlated Systems: Real Space Pairing and Statistically Consistent Mean-Field Theory - in Perspective
Autorzy:
Spałek, J.
Powiązania:
https://bibliotekanauki.pl/articles/1431227.pdf
Data publikacji:
2012-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.27.+a
74.70.Tx
74.20.-z
Opis:
In this brief overview we discuss the principal features of real space pairing as expressed via corresponding low-energy (t-J or periodic Anderson-Kondo) effective Hamiltonian, as well as consider concrete properties of those unconventional superconductors. We also rise the basic question of statistical consistency within the so-called renormalized mean-field theory. In particular, we provide the phase diagrams encompassing the stable magnetic and superconducting states. We interpret real space pairing as correlated motion of fermion pair coupled by short-range exchange interaction of magnitude J comparable to the particle renormalized band energy ≈ tx, where x is the carrier number per site. We also discuss briefly the difference between the real-space and the paramagnon-mediated sources of superconductivity. The paper concentrates both on recent novel results obtained in our research group, as well as puts the theoretical concepts in a conceptual as well as historical perspective. No slave-bosons are required to formulate the present approach.
Źródło:
Acta Physica Polonica A; 2012, 121, 4; 764-784
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical Approach to Strongly Correlated Systems Based on the U(1) and SU(2) Symmetry Groups
Autorzy:
Kopeć, T.
Powiązania:
https://bibliotekanauki.pl/articles/1431186.pdf
Data publikacji:
2012-04
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.20.Fg
71.10.Pm
Opis:
The spin-rotationally invariant SU(2)×U(1) approach to the Hubbard model is extended to accommodate the charge degrees of freedom. Both U(1) and SU(2) gauge transformation are used to factorize the charge and spin contribution to the original electron operator in terms of the emergent gauge fields. By tracing out gauge bosons the form of paired states is established and the role of antiferromagnetic correlations is explicated. We argue that in strongly correlated electron system collective instanton excitations of the phase field (dual to the charge) arise with a great degree of stability, governed by gauge flux changes by an integer multiple of 2π. Furthermore, it is shown that U(1) and SU(2) gauge fields play a similar role as phonons in the BCS theory: they act as the the "glue" for fermion pairing.
Źródło:
Acta Physica Polonica A; 2012, 121, 4; 738-743
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Theoretical Analysis of the Short Coherence Length Superconductors
Autorzy:
Wysokiński, K.
Ciechan, A.
Krzyszczak, J.
Powiązania:
https://bibliotekanauki.pl/articles/1536554.pdf
Data publikacji:
2010-08
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
71.10.Fd
74.20.-z
74.81.-g
Opis:
Properties of the short coherence length ξ superconductors are markedly different from those with long ξ. The main difference is connected with their response to impurities. Even the s-wave superconductors have been predicted not to obey the so-called Anderson theorem and to show appreciable fluctuations of order parameter. This observation has been recently confirmed in a number of beautiful scanning tunnelling experiments on high temperature cuprate and pnictide superconductors. In this work we study clean two-band systems within BCS-type approach and impure superconductors within mean field Bogolubov-de Gennes approach. In the weak disorder limit both s-wave and d-wave superconductors only weakly react to impurities. Presence of the Van Hove singularities in the density of states of the two-band clean systems strongly increases their superconducting transition temperature if the intra-band pair scattering is the only pairing interaction. The effect of impurities on such superconductors does depend on the sign of the inter-orbital interaction.
Źródło:
Acta Physica Polonica A; 2010, 118, 2; 232-237
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:
The Polaron Scenario for High-T$\text{}_{c}$ Superconductivity
Autorzy:
Ranninger, J.
Powiązania:
https://bibliotekanauki.pl/articles/1860957.pdf
Data publikacji:
1994-01
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.+z
71.38.+i
67.20.+k
Opis:
On the basis of experimental evidence we conclude that high-T$\text{}_{c}$ superconducting materials are composed of two distinct subsystems: one in which electrons are bound together in form of localized pairs of small polarons (bipolarons) and one in which electrons exist as strongly correlated Fermions. Upon doping one passes at a critical doping rate from the insulating parent compounds to metallic compounds. There, a charge transfer mechanism between the two subsystems sets in abruptly by which bipolarons can decay into pairs of electrons and vice versa. Such a picture can be modelled by a mixture of interacting Bosons and Fermions. A superconducting ground state for such a system develops at low temperature which is characterized by the opening of a gap in the single electron spectrum and the appearance of collective Boson excitations with a linear spectrum which is confined to the energy regime of the gap. Above T$\text{}_{c}$, a pseudo-gap remains upon closing the superconducting gap. There are strong indications that the normal state has non Fermi liquid behaviour.
Źródło:
Acta Physica Polonica A; 1994, 85, 1; 89-102
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Form of Energy Gap and Critical Temperature of Superconductor Implied by Fluctuations of Density of States
Autorzy:
Gładysiewicz, M.
Gonczarek, R.
Mulak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2014021.pdf
Data publikacji:
2000-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
Opis:
The s-paired BCS superconductor with the electron density of states depending on energy in the vicinity of Fermi level is considered. The existence of such fluctuations of electron density of states may be referred to Van Hove singularities widely discussed in the literature. In the paper three types of small fluctuations of the electron density of states introduced about its average background's value are analysed: Lorentzian, triangle, and logarithmic ones. In order to calculate numerically the energy gap and critical temperature, the formalism of parametric BCS gap equations is applied. The positive fluctuations (peaks) correspond to the increase in occupied states number inducing a higher critical temperature. On the other hand, negative fluctuations, which decrease the number of occupied states, lead to a lower critical temperature. Such decrease in critical temperature can lead, at a specific choice of parameters, to the decease in superconductivity. The presence of fluctuations finds reflection in the shape of energy gap as a function of temperature. In the vicinity of T=0 an abrupt decrease or increase in the energy gap to the original BCS value, according to the sign of the fluctuation, is observed. In turn, the fluctuations do not change the behaviour of the energy gap near T$\text{}_{c}$.
Źródło:
Acta Physica Polonica A; 2000, 97, 6; 1039-1051
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Form and Properties of the Tight-Binding Density of States in Two Dimensions. Possible Application to Superconductivity
Autorzy:
Gładysiewicz, M.
Gonczarek, R.
Mulak, M.
Powiązania:
https://bibliotekanauki.pl/articles/2030728.pdf
Data publikacji:
2002-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.20.Fg
Opis:
The form of the density of states for a tight-binding model with the first and the next-nearest neighbour hoppings for a rectangular planar lattice and a shift of the chemical potential are calculated. This is newly and comprehensively formulated integral form illustrated numerically, helpful in approach to two-dimensional superconducting models. In some particular cases the complete analytical forms of the density of states are obtained. It is shown that for all cases the density of states has a single van Hove singularity of the logarithmic type at the identically defined point. The proper approximate analytical representations are found. The difference between the exact numerical and approximate analytical forms is evaluated and illustrated.
Źródło:
Acta Physica Polonica A; 2002, 101, 6; 865-874
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Existence of the 60 K Plateau in the YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ Phase Diagram: the Role of Oxygen Ordering and Charge Imbalance
Autorzy:
Zaleski, T. A.
Kopeć, T. K.
Powiązania:
https://bibliotekanauki.pl/articles/2047332.pdf
Data publikacji:
2007-05
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.-z
74.72.Bk
74.62.-c
Opis:
We propose a semi-microscopic model of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ to investigate the origin of the 60 K plateau in its phase diagram. Our model is a "phase only" approach to the high-temperature superconducting system in terms of collective variables. It is able to capture characteristic energy scales present in YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ by using adjustable parameters representing phase stiffnesses and allows for strong anisotropy within basal planes to simulate oxygen ordering. We solve the model calculated T$\text{}_{c}$ for chosen system parameters investigating the influence of oxygen ordering and doping imbalance on the shape of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ phase diagram. Our results suggest that the oxygen ordering alone does not seem to be responsible for the existence of the 60 K plateau. However, relying on experimental data unveiling that oxygen doping of YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ may introduce a significant charge imbalance between CuO$\text{}_{2}$ planes and other sites, we show that simultaneously the former are underdoped, while the latter - strongly overdoped almost in the whole region of oxygen doping in which YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{6+y}$ is superconducting. This provides two natural counter acting factors, which possibly lead to rise the 60 K plateau with increasing oxygen doping.
Źródło:
Acta Physica Polonica A; 2007, 111, 5; 705-711
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Temperature Dependence of the Electron Raman Light Scattering in Normal Metals and Superconductors
Autorzy:
Falkovsky, L.
Klama, S.
Powiązania:
https://bibliotekanauki.pl/articles/1930519.pdf
Data publikacji:
1994-02
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
74.20.Fg
74.20.-z
78.30.Er
Opis:
Within the anisotropic BCS model the temperature dependence of the electron Raman light scattering in normal metals and superconductors is investigated. In either case analytical expressions describing the intensity of scattered light as a function of the Raman frequency and temperature are derived.
Źródło:
Acta Physica Polonica A; 1994, 85, 2; 311-315
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
Wyświetlanie 1-15 z 89

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