scholarly journals A simple mechanism for unconventional superconductivity in a repulsive fermion model

2019 ◽  
Vol 6 (2) ◽  
Author(s):  
Kevin Slagle ◽  
Yong Baek Kim
Keyword(s):  
Cooper Pair ◽  
Energy Gap ◽  
Tight Binding ◽  
Hard Core ◽  
Particle Energy ◽  
Bcs Theory ◽  
Unconventional Superconductivity ◽  
Fermion Model ◽  
Repulsive Interactions ◽  
Degenerate Perturbation Theory

Motivated by a scarcity of simple and analytically tractable models of superconductivity from strong repulsive interactions, we introduce a simple tight-binding lattice model of fermions with repulsive interactions that exhibits unconventional superconductivity (beyond BCS theory). The model resembles an idealized trilayer. The Cooper pair consists of electrons on opposite sides of the dielectric, which mediates the attraction. In the strong coupling limit, we use degenerate perturbation theory to show that the model reduces to a superconducting hard-core Bose-Hubbard model. Above the superconducting critical temperature, an analog of pseudo-gap physics results where the fermions remain Cooper paired with a large single-particle energy gap.

GENERALIZED BCS EQUATIONS: APPLICATIONS

2010 ◽  
Vol 24 (19) ◽  
pp. 3701-3712 ◽  
Author(s):  
G. P. MALIK
Keyword(s):  
Cooper Pair ◽  
Energy Gap ◽  
High Temperature Superconductors ◽  
Bcs Theory ◽  
Simple Extension ◽  
Cooper Pairs ◽  
Debye Temperatures ◽  
Unified Study ◽  
Interesting Candidate ◽  
Composite Superconductors

Based on the concepts of a superpropagator, multiple Debye temperatures, and equivalence of the binding energy of a Cooper pair and the BCS energy gap, the set of generalized BCS equations obtained recently via a temperature-generalized Bethe–Salpeter equation is employed for a unified study of the following composite superconductors: MgB 2, Nb 3 Sn , and YBCO. In addition, we study the Nb – Al system in which Cooper pairs as resonances have recently been reported to have been observed. Our approach seems to suggest that a simple extension of the BCS theory that accommodates the concept of Cooper pairs bound via a more than one phonon exchange mechanism may be an interesting candidate for dealing with high-temperature superconductors.

ON THE EQUIVALENCE OF THE BINDING ENERGY OF A COOPER PAIR AND THE BCS ENERGY GAP: A FRAMEWORK FOR DEALING WITH COMPOSITE SUPERCONDUCTORS

2010 ◽  
Vol 24 (09) ◽  
pp. 1159-1172 ◽  
Author(s):  
G. P. MALIK
Keyword(s):  
Binding Energy ◽  
Cooper Pair ◽  
Energy Gap ◽  
Direct Consequence ◽  
Bcs Theory ◽  
Subsequent Paper ◽  
Hartree Fock ◽  
Composite Superconductors ◽  
The One ◽  
Particle Propagator

Employing the Bethe–Salpeter equation (BSE) and the Matsubara recipe, and invoking both the electron–electron and the hole–hole scattering channels, we establish that the binding energy (W) of a Cooper pair (CP) is real, and equals the BCS energy gap (Δ) for all T ≤ Tc for a one-component superconductor. Given that the BCS theory is a generalization of the Hartree–Fock theory (generalized to allow for particle number fluctuations), the cognescenti would expect this result as a direct consequence of Koopman's theorem, proved for and well-known in the latter theory. However, this theorem is seldom mentioned in the literature on superconductivity; on the contrary, there is the statement in well-known texts that the binding energy of a CP becomes imaginary when the above-stated scattering channels are invoked for their formation. The importance of |W| = |Δ| for high-Tc superconductors is brought out by replacing the one-particle propagator in the BSE by a superpropagator — a field-theoretic construct apt for dealing with composite superconductors (CSs). A set of generalized BCS equations is thus obtained which, with the input of the multiple gaps of a CS, enables one to calculate its Tc uniquely. Applications of these equations will be taken up in a subsequent paper.

ENERGY GAP DEPENDENCE ON ANION CONCENTRATION FOR GaxIn1-xAsyP1-y QUATERNARY ALLOY BY RECURSION METHOD

2004 ◽  
Vol 18 (18) ◽  
pp. 955-962
Author(s):  
MUSA EL-HASAN ◽  
REZEK ESTATIEH
Keyword(s):  
Density Of States ◽  
Energy Gap ◽  
Local Density ◽  
Tight Binding ◽  
Quaternary Alloy ◽  
Average Density ◽  
Local Density Of States ◽  
Recursion Method ◽  
Orbital Decomposition ◽  
Lattice Matched

Three terminators have been tested, square root terminator, quadreture terminator and linear terminator, it was found that the linear terminator is the best, so it was used in calculating local density of states (LDOS) and it's orbital decomposition, alloy average density of states, and energy gap for different anion concentrations for InP lattice matched alloy. The results were compared with our previous calculations of (LDOS), and results from other methods. Energy gap was compared with experimental measurements. A five orbital sp3s* per atom model was used in the tight-binding representation of the Hamiltonian.

scholarly journals Cluster crystals with combined soft- and hard-core repulsive interactions

2018 ◽  
Vol 98 (5) ◽  
Author(s):  
Lorenzo Caprini ◽  
Emilio Hernández-García ◽  
Cristóbal López
Keyword(s):  
Hard Core ◽  
Repulsive Interactions

THEORETICAL APPROACH USING EXTENDED HUCKEL TIGHT-BINDING METHOD OF THE ELECTRONIC STRUCTURE OF CeOs4Sb12 FILLED SKUTTERUDITE

2006 ◽  
Vol 20 (08) ◽  
pp. 1005-1014
Author(s):  
DONALD H. GALVAN ◽  
J. C. SAMANIEGO
Keyword(s):  
Heavy Fermion ◽  
Energy Gap ◽  
Population Analysis ◽  
Tight Binding ◽  
Energy Bands ◽  
Mulliken Population ◽  
Semiconductor Behavior ◽  
Tight Binding Method ◽  
Strong Hybridization ◽  
Heavy Fermion Behavior

Based on band structure, total and projected density of states and Mulliken Population Analysis, the electronic properties of CeOs 4 Sb 12 were investigated. The calculated energy bands depict a semiconductor behavior with an energy gap (direct gap at H ) of the order of 0.45 eV. On the other hand, a strong hybridization occurs between Ce f-orbitals with Os d-, p-, and Sb p-orbitals, which convince us to believe that this hybridization, added to the existence of a mini gap, are responsible for the heavy Fermion behavior, as well as the possibility to consider it a candidate for thermoelectric applications.

Entropy and heat capacity in the generalized Bose–Einstein condensation theory of superconductors

2019 ◽  
Vol 33 (26) ◽  
pp. 1950311
Author(s):  
L. A. García ◽  
M. de Llano
Keyword(s):  
Heat Capacity ◽  
Energy Gap ◽  
Coupling Parameter ◽  
Bcs Theory ◽  
Einstein Condensation ◽  
Cooper Pairs ◽  
Total Electron ◽  
Bose Einstein Condensation ◽  
Unpaired Electrons ◽  
Bose Einstein

The new generalized Bose–Einstein condensation (GBEC) quantum-statistical theory starts from a noninteracting ternary boson-fermion (BF) gas of two-hole Cooper pairs (2hCPs) along with the usual two-electron Cooper pairs (2eCPs) plus unpaired electrons. Here we obtain the entropy and heat capacity and confirm once again that GBEC contains as a special case the Bardeen–Cooper–Schrieffer (BCS) theory. The energy gap is first calculated and compared with that of BCS theory for different values of a new dimensionless coupling parameter n/n[Formula: see text] where n is the total electron number density and n[Formula: see text] that of unpaired electrons at zero absolute temperature. Then, from the entropy, the heat capacity is calculated. Results compare well with elemental-superconductor data suggesting that 2hCPs are indispensable to describe superconductors (SCs).

Electronic Structures of Oligomers of Pyrrole

2010 ◽  
Vol 663-665 ◽  
pp. 658-661 ◽  
Author(s):  
Bao Gai Zhai ◽  
Qing Lan Ma ◽  
Yuan Ming Huang
Keyword(s):  
Electronic Structures ◽  
Energy Gap ◽  
Tight Binding ◽  
One Dimensional ◽  
Extended Hückel ◽  
The Relationship ◽  
Green Photoluminescence

The electronic structures of oligomers of pyrrole have been calculated using the extended Hückel tight-binding program. The energy diagrams are shown for oligomers as the number of the repeating unit in the oligomers increases from 1 to 16. The relationship between the energy gap of the oligomers and the number of the repeating unit in the oligomers is established. Blue-green photoluminescence and electroluminescence from one-dimensional polypyrrole are predicted.

ENERGY GAP, MASS GAP, AND SPONTANEOUS SYMMETRY BREAKING

2010 ◽  
Vol 25 (22) ◽  
pp. 4141-4148 ◽  
Author(s):  
YOICHIRO NAMBU
Keyword(s):  
Symmetry Breaking ◽  
Spontaneous Symmetry Breaking ◽  
Particle Physics ◽  
Energy Gap ◽  
50Th Anniversary ◽  
Bcs Theory ◽  
Historical Overview ◽  
University Of Illinois ◽  
Mass Gap ◽  
The University

This article is based on a talk given at a Symposium at the University of Illinois on the occasion to commemorate the 50th anniversary of BCS — I gave a historical overview of how BCS theory has come to be transplanted to particle physics and has helped solve its problems.

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