Multiband superconductivity with competing intra- and interband pair channels

2016 ◽  
Vol 30 (13) ◽  
pp. 1642017
Author(s):  
N. Kristoffel ◽  
P. Rubin
Keyword(s):  
Mean Field ◽  
Equation System ◽  
Order Parameters ◽  
Band Model ◽  
Multiband Superconductivity ◽  
Complicated Structure ◽  
General Behaviour ◽  
Interband Interaction ◽  
Extremal Points ◽  
The Mean

In multiband superconductivity interband interaction channels creating the pairs of intraband [Formula: see text] and interband [Formula: see text] compositions can appear. Simultaneous functioning of these channels is investigated here. A three-band model where two similar bands [Formula: see text] interact with the itinerant-band has been proposed. The mean field Hamiltonian incorporates three order parameters [Formula: see text]; [Formula: see text]; [Formula: see text] genetically associated with dispersive bands. Calculated quasiparticle energies and operator averages lead to a coupled nonlinear equation system for the order parameters. Illustrative calculations versus temperature have been made for overlapping bands. At fixed parameters, the basic system has two independent solutions. The free energy has a complicated structure of extremal points. The interaction of channels with intra- and interband points is seen. These channels compete in general. From the point where the gap, type parameters associated with one channel become zero, the other continues as the first channel was logged out. The general behaviour of order parameters distribution is very sensible to [Formula: see text]. Events of critical nature appear. Weakening of [Formula: see text] stimulates the formation of closed bubbles built up by the same type parameters from different parallel solutions.

PHENOMENOLOGICAL THEORY OF HIGH Tc SUPERCONDUCTORS

1987 ◽  
Vol 01 (03n04) ◽  
pp. 997-1000 ◽  
Author(s):  
M.P. Das ◽  
A.G. Saif
Keyword(s):  
Electrical Conductivity ◽  
Mean Field ◽  
Phenomenological Theory ◽  
Phenomenological Approach ◽  
Order Parameters ◽  
High Tc Superconductors ◽  
High Tc ◽  
Field Approach ◽  
Superconducting Ceramics ◽  
The Mean

We present a phenomenological approach in terms of two coexisting macroscopic order parameters correponding to the superconducting and the insulating states relevant to the high. temperature superconducting ceramics. On using the mean field approach we discuss the electrodynamical responses and from the fluctuations of the order parameters we obtain results for the electrical conductivity, which is shown to possess anomalies as in the granular materials.

Anisotropic Order Parameter in Two-Band Superconductivity

1998 ◽  
Vol 12 (29n31) ◽  
pp. 3099-3101 ◽  
Author(s):  
P. Konsin ◽  
N. Kristoffel ◽  
P. Rubin
Keyword(s):  
Order Parameter ◽  
Equation System ◽  
Order Parameters ◽  
Band Model ◽  
Gap Equation ◽  
Narrow Region ◽  
Interband Scattering ◽  
Parameter Symmetry ◽  
Order Parameter Symmetry

A two-overlapping band model of superconductivity with s+d interband scattering is investigated. The gap equation system has been solved numerically. Solutions of pure-d and -s, or of mixed s+d nature are possible. The pure Tcd(μ) or Tcs(μ) curves determine the onset of superconductivity with temperature lowering. In the under- and over-doped region pure-symmetry orderings are preferred. Mixed ordering can exist in a narrow region of μ, becoming narrower with T rising. The peculiarities of the and spectra are reflected in the behaviour of the order parameters. Order parameter symmetry can change with T and μ.

Quantum phase crossover in the spherical mean-field plus quadrupole–quadrupole and pairing model with two j-orbits

2020 ◽  
Vol 29 (06) ◽  
pp. 2050039
Author(s):  
Bo Li ◽  
Feng Pan ◽  
Xiao-Xue Ding ◽  
J. P. Draayer
Keyword(s):  
Mean Field ◽  
Order Parameters ◽  
Quantum Phase ◽  
Simple Description ◽  
Effective Order ◽  
Spherical Mean ◽  
Crossover Behavior ◽  
Pairing Model ◽  
The Mean

The shape phase crossover in the mean-field plus the geometric quadrupole–quadrupole and pairing model within two [Formula: see text]-orbits is analyzed, for which a simple description of [Formula: see text]Sn confined in the lowest [Formula: see text] and [Formula: see text] orbits above the [Formula: see text]Sn core is demonstrated to reveal the crossover behavior of the model. It is shown that [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] in this case may serve as effective order parameters for even–even and odd-A systems, respectively, from which the shape phase crossover from the rotation-like phase to the superconducting-like phase can be observed with variation of the number of valence neutrons.

FLUCTUATION EFFECTS IN A CLASS OF SYSTEMS WITH TWO ORDER PARAMETERS

1993 ◽  
Vol 07 (27) ◽  
pp. 1725-1731 ◽  
Author(s):  
L. DE CESARE ◽  
I. RABUFFO ◽  
D.I. UZUNOV
Keyword(s):  
Phase Transition ◽  
Renormalization Group ◽  
Phase Transitions ◽  
Order Phase Transition ◽  
Mean Field ◽  
Ising Models ◽  
Order Parameters ◽  
The Mean ◽  
Fluctuation Effects ◽  
Second Order Phase Transition

The phase transitions described by coupled spin -1/2 Ising models are investigated with the help of the mean field and the renormalization group theories. Results for the type of possible phase transitions and their fluctuation properties are presented. A fluctuation-induced second-order phase transition is predicted.

The nuclear relaxation rate for the itinerant-electron antiferromagnet

1982 ◽  
Vol 60 (5) ◽  
pp. 649-653 ◽  
Author(s):  
M. Crişan ◽  
Zs. Gulácsi
Keyword(s):  
Field Theory ◽  
Relaxation Rate ◽  
Mean Field Theory ◽  
Mean Field ◽  
Band Model ◽  
Itinerant Electron ◽  
Nuclear Relaxation ◽  
The Mean ◽  
Two Band Model ◽  
Good Agreement

The relaxation rate in the nuclear magnetic resonance of the itinerant-electron antiferromagnet was calculated as a function of temperature. A good agreement with the experimental results obtained on CrB2 has been observed. The two band model for the itinerant-electron antiferromagnet for T < TN (TN is the critical temperature) and the mean field theory for the critical region have been used to calculate [Formula: see text] as a function of temperature.

Mean-Field Analysis of the Three-Band Hubbard Model

1998 ◽  
Vol 12 (27n28) ◽  
pp. 2831-2845 ◽  
Author(s):  
Yabin Yu ◽  
Guanghan Cao ◽  
Zhengkuan Jiao
Keyword(s):  
Electronic Structure ◽  
Hubbard Model ◽  
Singlet State ◽  
Mean Field ◽  
Coulomb Repulsion ◽  
Mean Field Approximation ◽  
Band Model ◽  
Spin Singlet ◽  
Half Filling ◽  
The Mean

A full three-band model for the CuO 2 plane of cuprates, which includes all the essential interaction — Cu-O and O-O hopping and the Coulomb repulsion on the Cu and O sites and between them, is considered. Its antiferromagnetic ground state for the half-filling is studied by using the mean field approximation. The electronic structure and the magnetic properties such as the densities of states, the energy spectra, the composition of holes (Cu or O character), the superexchange interaction and the magnetic moment are calculated and in general, our results are in agreement with the available experimental and other calculation results. Meanwhile, we find that the influence of the O-O hopping and Cu-O intrasite Coulomb repulsion on these properties is considerable. Our estimate of the energy of the spin singlet state above the antiferromagnetic background indicates that the lowest excitation state of the holes is the singlet state and give a charge-transfer energy in agreement with the experiment. We also discuss the hole-doping to the antiferromagnetic background and find the mean field approach invalid. Finally, based on the electronic structure at the half-filling, en effective one-band Hubbard model is presented and the effective parameters are close to the values given by the computation on the clusters.

Molecular Polarizabilities and Orientational Ordering of Two Mesogens

1991 ◽  
Vol 46 (10) ◽  
pp. 858-864 ◽  
Author(s):  
M. Mitra ◽  
S. Paul ◽  
R. Paul
Keyword(s):  
Field Theory ◽  
Liquid Crystalline ◽  
Mean Field Theory ◽  
Orientational Order ◽  
Mean Field ◽  
Continuum Theory ◽  
Order Parameters ◽  
Liquid Phases ◽  
Molecular Polarizabilities ◽  
The Mean

AbstractThe refractive indices (no, ne) and densities of two mesogens have been measured in their liquid crystalline and liquid phases. The molecular polarizabilities (xo, xe) were evaluated by Vuks' and Neugebauer's relations. The polarizabilities thus obtained are compared with those estimated from the bond polarizabilities, and the orientational order parameters, <P2>, are compared with the mean field theory of Maier and Saupe, the modified mean field theory of Humphries, James and Luckhurst. and the continuum theory suggested by T. E. Faber. We have also calculated the three order parameters (<P2), τ, σ) describing the smectic A phase following McMillan's model. Possible causes of the discrepancy are discussed.

ANALYTICAL EXPRESSIONS OF THE ORDER PARAMETERS NEAR THE TRANSITION TEMPERATURES IN THE SPIN-3/2 ISING SYSTEM WITH BILINEAR AND BIQUADRATIC INTERACTIONS

2006 ◽  
Vol 20 (04) ◽  
pp. 455-467 ◽  
Author(s):  
OSMAN CANKO ◽  
MUSTAFA KESKIN
Keyword(s):  
Phase Transitions ◽  
Mean Field ◽  
Field Approximation ◽  
Irreversible Thermodynamics ◽  
Order Parameters ◽  
Mean Field Approximation ◽  
Transition Temperatures ◽  
Ising System ◽  
The Mean ◽  
Analytical Expressions

Analytical expressions of the order parameters near the transition temperatures in the spin-3/2 Ising system with bilinear (J) and biquadratic (K) interactions are presented for various values of J/K. First, we obtain the free energy expression and the equations to determine order parameters by using the mean-field approximation. Then, the order parameters are expressed in the vicinity of the transition temperatures in which these expressions are very important to study the dynamics of the system by means of Onsager's theory of irreversible thermodynamics. Hence, we investigate the phase transitions occurring in the system and also obtain two tricritical points analytically. Finally, the specific heat and magnetic susceptibility are calculated and an argument about the critical exponents at the second-order phase transitions and tricritical points is given.

scholarly journals SUSCEPTIBILITIES AND THE PHASE STRUCTURE OF AN EFFECTIVE CHIRAL MODEL WITH POLYAKOV LOOPS

2007 ◽  
Vol 16 (07n08) ◽  
pp. 2319-2324
Author(s):  
CHIHIRO SASAKI ◽  
BENGT FRIMAN ◽  
KRZYSZTOF REDLICH
Keyword(s):  
Phase Transitions ◽  
Phase Structure ◽  
Mean Field ◽  
Field Approximation ◽  
Order Parameters ◽  
Mean Field Approximation ◽  
Chiral Model ◽  
Chiral Phase ◽  
The Mean ◽  
Polyakov Loops

In the Nambu–Jona-Lasinio model with Polyakov loops, we explore the relation between the deconfinement and chiral phase transitions within the mean-field approximation. We focus on the phase structure of the model and study the susceptibilities associated with corresponding order parameters.

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