ENERGY BAND OVERLAPPING IN HIGH-Tc SUPERCONDUCTORS

1996 ◽  
Vol 10 (30) ◽  
pp. 1483-1490 ◽  
Author(s):  
M. MORENO ◽  
R. M. MÉNDEZ-MORENO ◽  
M. A. ORTIZ ◽  
S. OROZCO
Keyword(s):  
Weak Coupling ◽  
Cuprate Superconductors ◽  
Weak Coupling Limit ◽  
Band Model ◽  
Coupling Constant ◽  
High Tc Superconductors ◽  
Energy Bands ◽  
Effective Coupling ◽  
High Tc ◽  
Two Band Model

Multi-band superconductors are analyzed and the relevance of overlapping energy bands to the high-T c of these materials is studied. Within the BCS framework, a two band model with generalized Fermi surface topologies is developed. Values of the overlapped occupancy parameters for typical cuprate superconductors are obtained as a function of the ratio R and the effective coupling constant, λ, in the weak-coupling limit. The overlap scale is of the order or lower than the cutoff (Debye) energy. The typical behavior of the isotope effect is obtained. As these superconductors have transition temperatures above the phonon barrier, the results of this approach are important to the generic understanding of the high-T c superconducting mechanism.

MERCURY-BASED SUPERCONDUCTORS WITH QUASI-NORMAL OCCUPANCY

1995 ◽  
Vol 09 (18) ◽  
pp. 1175-1184
Author(s):  
M. MORENO ◽  
R.M. MÉNDEZ-MORENO ◽  
S. OROZCO ◽  
M.A. ORTÍZ
Keyword(s):  
Transition Temperature ◽  
Fermi Surface ◽  
Weak Coupling ◽  
Cuprate Superconductors ◽  
Energy Gap ◽  
Oxide Superconductors ◽  
Coupling Constant ◽  
Effective Coupling ◽  
Small Energy ◽  
Copper Oxide Superconductors

A model with anomalous occupancy is applied to Hg-based cuprate superconductors. The anomaly consists of a small energy gap near the Fermi surface, the scale of the gap anomaly is of order of the cutoff (v.g. Debye) energy. Values of the anomalous occupancy parameters for Hg-based superconductors are obtained for different values of the ratio R and the effective coupling constant, within the weak coupling. As these materials have the highest transition temperature known for layered copper-oxide superconductors, they serve as a new testing ground for various proposed models.

Grain Boundary Modelling and Correlation with Critical Current Densities in High‐Tc Superconductors

1989 ◽  
Vol 169 ◽  
Author(s):  
K. Jagannadham ◽  
J. Narayan
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Weak Coupling ◽  
Weak Coupling Limit ◽  
Excess Charge ◽  
High Tc Superconductors ◽  
High Tc ◽  
Geometrical Modelling ◽  
Current Densities

AbstractGeometrical modelling of grain boundaries in 123‐YBaCuO and 2223‐TlBaCaCuO systems is carried out for several misorientat‐ions. The a‐b and the a‐c type coincidence boundaries are analyzed to determine the fraction of Cu‐O planes that are continuous and the excess charge present at the boundary voids. The interg‐rain critical current density is determined as a function of the misorientation and the width of the boundary. The tunneling of superconductor pairs through the regions of distortions, giving rise to depression of the order parameter at the boundaries,is used to determine the critical current density in the weak coupling limit.

scholarly journals Character of Doped Holes in Nd1−xSrxNiO2

2021 ◽  
Vol 6 (3) ◽  
pp. 33
Author(s):  
Tharathep Plienbumrung ◽  
Michael Thobias Schmid ◽  
Maria Daghofer ◽  
Andrzej M. Oleś
Keyword(s):  
Rare Earth ◽  
Charge Transfer ◽  
Charge Distribution ◽  
Hole Doping ◽  
Band Model ◽  
High Tc Superconductors ◽  
Transfer Energy ◽  
High Tc ◽  
Charge Transfer Energy ◽  
Two Band Model

We investigate charge distribution in the recently discovered high-Tc superconductors, layered nickelates. With increasing value of charge-transfer energy, we observe the expected crossover from the cuprate to the local triplet regime upon hole doping. We find that the d−p Coulomb interaction Udp makes Zhang-Rice singlets less favorable, while the amplitude of local triplets at Ni ions is enhanced. By investigating the effective two-band model with orbitals of x2−y2 and s symmetries we show that antiferromagnetic interactions dominate for electron doping. The screened interactions for the s band suggest the importance of rare-earth atoms in superconducting nickelates.

scholarly journals Effective electromagnetic lagrangian at finite temperature and density in the electroweak model

Open Physics ◽  
2011 ◽  
Vol 9 (4) ◽  
Author(s):  
Andrea Erdas
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Partition Function ◽  
Field Strength ◽  
Constant Magnetic Field ◽  
Finite Temperature ◽  
Weak Coupling ◽  
Weak Coupling Limit ◽  
Effective Coupling ◽  
Electroweak Model

AbstractUsing the exact propagators in a constant magnetic field, the effective electromagnetic lagrangian at finite temperature and density is calculated to all orders in the field strength B within the framework of the complete electroweak model, in the weak coupling limit. The partition function and free energy are obtained explicitly and the finite temperature effective coupling is derived in closed form. Some implications of this result, potentially interesting to astrophysics and cosmology, are discussed.

The influence of oxygen disorder on high-Tc superconductivity in two-band model

1989 ◽  
Vol 69 (7) ◽  
pp. 747-750 ◽  
Author(s):  
V.A. Moskalenko ◽  
M.E. Palistrant ◽  
V.M. Vaekaluk ◽  
I.V. Padure
Keyword(s):  
Band Model ◽  
High Tc ◽  
High Tc Superconductivity ◽  
Two Band Model

BCS-LIKE APPROXIMATION IN A TWO-BAND MODEL FOR SUPERCONDUCTIVITY IN MgB2

2005 ◽  
Vol 19 (11) ◽  
pp. 503-516 ◽  
Author(s):  
EUGEN-VICTOR MACOCIAN
Keyword(s):  
Critical Temperature ◽  
Weak Coupling ◽  
Analytical Calculation ◽  
Gap Functions ◽  
Band Model ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Multiband Model ◽  
Two Band Model ◽  
Interband Coupling

The BCS limit of a two-band model for superconductivity in MgB 2 is discussed and the temperature dependence of the gap functions is calculated together with their values at T = 0. We have studied the effect of interband coupling on the order parameters and critical temperature. The validity of the approximation was investigated by direct comparison with more accurate Eliashberg calculation and it was found that the BCS-like model is appropriate for temperatures up to T ~ 10 K . The two-band superconductivity in MgB 2 has been extensively studied in the literature, in Eliashberg or weak-coupling calculations, as well as in ab initio evaluations of electron–phonon interaction. Here we find from an analytical calculation the well known result that the ratio 2Δ/Tc is no longer universal in the multiband model, in contrast with the classical single-band BCS model.

CRITICAL TEMPERATURE OF HIGH-Tc SUPERCONDUCTORS AND BOUNDARY CONDITIONS IN GINZBURG-LANDAU THEORY

2009 ◽  
Vol 23 (20n21) ◽  
pp. 4269-4276 ◽  
Author(s):  
A. LYKOV
Keyword(s):  
Boundary Condition ◽  
Critical Temperature ◽  
Order Parameter ◽  
Cuprate Superconductors ◽  
Landau Theory ◽  
Structural Elements ◽  
High Tc Superconductors ◽  
Ginzburg Landau ◽  
High Tc ◽  
Insulating Properties

New boundary condition for the order parameter in the Ginzburg-Landau theory is applied to the case of CuO 2 planes which are the main structural elements responsible for superconductivity in high-Tc superconductors. It was found that the order parameter in these superconductors is significantly depressed in the CuO 2 planes. As a result, this boundary condition to the GL equations is found to limit the critical temperature of high-Tc superconductors. Thus, in order to increase Tc of cuprate superconductors, the number of CuO 2 planes that are within a short distance of each other in unit cell or insulating properties of the layers located in the vicinity to the CuO 2 planes should be increased.

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