Superconductivity

Quantum 20/20 ◽  
2019 ◽  
pp. 261-284
Author(s):  
Ian R. Kenyon
Keyword(s):  
Energy Gap ◽  
Bose Condensate ◽  
Microscopic Theory ◽  
Meissner Effect ◽  
Bcs Theory ◽  
Type Ii ◽  
Josephson Effects ◽  
Condensation Energy ◽  
Voltage Standard ◽  
Condensate Phase

Superconductivity and the associated Meissner effect are introduced, indicating that superconductors are perfect diamagnetics. Condensation energy is deduced. The London analysis showing how superconductors exclude flux is presented. The BCS microscopic theory is recapitulated: Cooper pairs of electrons are the constituents of the Bose condensate that carries the non-dissipative current. The binding energy of pairs (energy gap below the Fermi sea) is deduced and related to their size and the critical temperature. Dependence of the energy gap on temperature is shown consistent with BCS theory. The Ginzberg–Landau analysis and the spontaneous symmetry breaking in the condensate phase are recounted. Quantization of trapped magnetic flux is shown to be related to superconductor topology. Type-II superconductors are treated. Finally Josephson effects show unambiguously that the condensate is a macroscopic quantum state. Josephson applications are enumerated, including a new voltage standard, SQUIDs and preliminary versions of qubits (transmons) for quantum computing.

Superconductivity

2018 ◽  
Author(s):  
L. Solymar ◽  
D. Walsh ◽  
R. R. A. Syms
Keyword(s):  
Energy Gap ◽  
Meissner Effect ◽  
Important Application ◽  
Type I ◽  
Type Ii ◽  
Type Ii Superconductors ◽  
Josephson Tunnelling ◽  
High Transition ◽  
Heat Of Transition ◽  
The Difference

The Meissner effect is discussed. The latent heat of transition is derived by a thermodynamic approach. The concept of surface energy is introduced, leading to the distinction between Type I and Type II superconductors. The differential equation for the superconducting wave function is derived. The energy gap and the phenomenon of tunnelling are discussed. The difference between superconducting tunnelling and Josephson tunnelling is explained. The significance of high transition temperature superconductors is discussed. It is shown that an important application of superconductors is to produce high-field magnets.

Superconducting State

2021 ◽  
Author(s):  
Vladimir Kresin ◽  
Sergei Ovchinnikov ◽  
Stuart Wolf
Keyword(s):  
Critical Temperature ◽  
Energy Gap ◽  
Microscopic Theory ◽  
Record Values ◽  
Theoretical Treatment ◽  
Many Body ◽  
Many Body Theory ◽  
Current State ◽  
Superconducting Compounds ◽  
Body Theory

For the past almost fifty years, scientists have been trying to explain the phenomenon of superconductivity. The mechanism is the key ingredient of microscopic theory, which was developed by Bardeen, Cooper, and Schrieffer in 1957. The theory also introduced the basic concepts of pairing, coherence length, energy gap, and so on. Since then, microscopic theory has undergone an intensive development. This book provides a very detailed theoretical treatment of the key mechanisms of superconductivity, including the current state of the art (phonons, magnons, plasmons). In addition, the book contains descriptions of the properties of the key superconducting compounds that are of the most interest for science and applications. For many years, there has been a search for new materials with higher values of the main parameters, such as the critical temperature and critical current. At present, the possibility of observing superconductivity at room temperature has become perfectly realistic. That is why the book is especially concerned with high-Tc systems such as high-Tc oxides, hydrides with record values for critical temperature under high pressure, nanoclusters, and so on. A number of interesting novel superconducting systems have been discovered recently, including topological materials, interface systems, and intercalated graphene. The book contains rigorous derivations based on statistical mechanics and many-body theory. The book also provides qualitative explanations of the main concepts and results. This makes the book accessible and interesting for a broad audience.

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).

FERMIONIC SUPERCONDUCTIVITY IN THE DENSE WEINBERG-SALAM MODEL

1990 ◽  
Vol 05 (17) ◽  
pp. 3417-3448 ◽  
Author(s):  
E.J. FERRER ◽  
V. DE LA INCERA ◽  
A.E. SHABAD
Keyword(s):  
Electromagnetic Field ◽  
Penetration Depth ◽  
Energy Gap ◽  
Polarization Operator ◽  
External Electromagnetic Field ◽  
Condensate Phase ◽  
Fermion Loop ◽  
Zero Momentum ◽  
The One

The superconducting behavior of the W-condensate phase of the Weinberg-Salam liquid is investigated. The removal of the W-orientation degeneracy by a small external electromagnetic field imposed on the W-condensate is found. Against the background of the condensed W-mesons the left-lepton spectrum undergoes a restructuring with the appearance of an energy gap between all the particle-antiparticle states, and the joining of particles and antiparticles in the new spectrum. Some of these peculiarities are indicated as a signal of the electrical superconductivity of such a medium. The definitive conclusions about the fermion superconductivity are achieved by studying the contribution to the London’s equation of the one-fermion loop polarization operator against the W-condensate background at zero momentum. The London’s penetration depth λ L is found in the limit of small W-condensate amplitude.

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.

scholarly journals Quantum magnetic monopole condensate

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
M. C. Diamantini ◽  
C. A. Trugenberger ◽  
V. M. Vinokur
Keyword(s):  
Bose Condensate ◽  
Meissner Effect ◽  
Magnetic Monopoles ◽  
Classical Electrodynamics ◽  
Cooper Pairs ◽  
Quantum Behavior ◽  
Magnetic Symmetry ◽  
Electric Analog ◽  
Classical Particles ◽  
Full Quantum

AbstractDespite decades-long efforts, magnetic monopoles were never found as elementary particles. Monopoles and associated currents were directly measured in experiments and identified as topological quasiparticle excitations in emergent condensed matter systems. These monopoles and the related electric-magnetic symmetry were restricted to classical electrodynamics, with monopoles behaving as classical particles. Here we show that the electric-magnetic symmetry is most fundamental and extends to full quantum behavior. We demonstrate that at low temperatures magnetic monopoles can form a quantum Bose condensate dual to the charge Cooper pair condensate in superconductors. The monopole Bose condensate manifests as a superinsulating state with infinite resistance, dual to superconductivity. The monopole supercurrents result in the electric analog of the Meissner effect and lead to linear confinement of the Cooper pairs by Polyakov electric strings in analogy to quarks in hadrons.

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.

scholarly journals Estimates of Impact Ionization Coefficients in Superlattice-Based Mid-Wavelength Infrared Avalanche Photodiodes

2003 ◽  
Vol 799 ◽  
Author(s):  
C. H. Grein ◽  
K. Abu El-Rub ◽  
M. E. Flatté ◽  
H. Ehrenreich
Keyword(s):  
Valence Band ◽  
Impact Ionization ◽  
Energy Gap ◽  
Avalanche Photodiodes ◽  
Threshold Energy ◽  
Type Ii ◽  
Band Engineering ◽  
Type Ii Superlattice ◽  
Low Threshold ◽  
Ionization Coefficients

ABSTRACTWe describe band engineering strategies to either enhance or suppress electron-initiated impact ionization relative to hole-initiated impact ionization in type II superlattice mid-wavelength infrared avalanche photodiodes. The strategy to enhance electron-initiated impact ionization involves placing a high density of states at approximately one energy gap above the bottom of the conduction band and simultaneously removing valence band states from the vicinity of one energy gap below the top of the valence band. This gives the electrons a low threshold energy and the holes a high one. The opposite strategy enhances hole-initiated impact ionization. Estimates of the electron (α) and hole (β) impact ionization coefficients predict that α/β>>1 in the first type of superlattice and α/β<<1 in the second type.

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