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Topic: BCS theory


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In the News (Wed 22 May 19)

  
  BCS theory
BCS theory was developed in 1957 by John Bardeen, Leon Cooper, and Robert Schrieffer, who received the Nobel Prize for Physics in 1972 as a result.
BCS theory starts from the assumption that there is some attraction between electrons, which can overcome the Coulomb repulsion.
BCS theory relates the value of the critical field at zero temperature to the value of the transition temperature and the density of states at the Fermi energy.
www.mcfly.org /BCS_theory   (830 words)

  
  BCS theory - Wikipedia, the free encyclopedia
BCS theory was developed in 1957 by John Bardeen, Leon Cooper, and Robert Schrieffer, who received the Nobel Prize for Physics in 1972 as a result.
BCS theory starts from the assumption that there is some attraction between electrons, which can overcome the Coulomb repulsion.
BCS theory relates the value of the critical field at zero temperature to the value of the transition temperature and the density of states at the Fermi energy.
en.wikipedia.org /wiki/BCS_theory   (898 words)

  
 Theory Feature @ NaturalResearch.org (Natural Research)   (Site not responding. Last check: 2007-10-26)
In science, a theory is a proposed description, explanation, or model of the manner of interaction of a set of natural phenomena, capable of predicting future occurrences or observations of the same kind, and capable of being tested through experiment or otherwise verified through empirical observation.
In this sense, a theory is a systematic and formalized expression of all previous observations that is predictive, logical and testable.
In the humanities, theory is often used as an abbreviation for critical theory or literary theory, referring to continental philosophy's aesthetics or its attempts to understand the structure of society and to conceptualize alternatives.
www.naturalresearch.org /encyclopedia/Theory   (2020 words)

  
 Effective field theory - Wikipedia, the free encyclopedia
In physics, an effective field theory is an approximate theory (usually a quantum field theory) that contains the appropriate degrees of freedom to describe physical phenomena occurring at a chosen length scale, but ignores the substructure and the degrees of freedom at shorter distances (or, equivalently, higher energies).
The theory had great phenomenological success and was eventually understood to arise from the gauge theory of electroweak interactions, which forms a part of the standard model of particle physics.
In this case the underlying theory is the theory of electrons in a metal interacting with lattice vibrations called phonons.
en.wikipedia.org /wiki/Effective_field_theory   (772 words)

  
 BCS theory is incorrect   (Site not responding. Last check: 2007-10-26)
The theory also implies that the electron-phonon interaction, assumed in BCS theory to be the cause of superconductivity, is in fact irrelevant to superconductivity.
BCS theory is unable to predict new superconductors because it assumes that superconductivity is associated with the electron-phonon interaction.
The theory of hole superconductivity predicts that superconductivity is associated with hole conduction in the normal state and that high Tc's occur when holes conduct in negatively charged structures, i.e.
www-physics.ucsd.edu /~jorge/bcs.html   (425 words)

  
 Superconductivity - Wikipedia   (Site not responding. Last check: 2007-10-26)
In 1950, the phenomenological Ginzburg-Landau theory[?] of superconductivity was devised by Landau and his student Ginzburg[?].
This BCS theory explained the superconducting current as a superfluid of "Cooper pairs", pairs of electrons interacting through the exchange of phonons.
The BCS theory was set on a firmer footing in 1958, when Bogoliubov showed that the BCS wavefunction, which had originally been derived from a variational argument, could be obtained using a canonical transformation of the electronic Hamiltonian.
wikipedia.findthelinks.com /su/Superconductivity.html   (1760 words)

  
 Quantum field theory - Wikipedia, the free encyclopedia
Non-relativistic quantum field theories are needed in condensed matter physics— for example in the BCS theory of superconductivity.
Relativistic quantum field theories are indispensable in particle physics (see the standard model), although they are known to arise as effective field theories in condensed matter physics.
For example, in every quantum theory the global phase of the wave function is arbitrary and does not represent something physical, so the theory is invariant under a global change of phases (adding a constant to the phase of all wave functions, everywhere); this is a global symmetry.
en.wikipedia.org /wiki/Quantum_field_theory   (4389 words)

  
 BCS Theory of Superconductivity
This evidence for a bandgap is one of the pieces of experimental evidence which supports the BCS theory of superconductivity.
This energy gap evidence was part of the experimental motivation for the BCS theory of superconductivity.
The value predicted for vanadium from its critical temperature of 5.38 K by the BCS theory is 1.6 meV, and the measured value is close to that.
hyperphysics.phy-astr.gsu.edu /hbase/solids/bcs.html   (723 words)

  
 BCS Theory for Conventional Superconductors   (Site not responding. Last check: 2007-10-26)
In 1957 the underlying microscopic theory of superconductivity in metals was unveiled by J. Bardeen, L.N. Cooper and J.R. Schrieffer [
BCS theory outlines how in the presence of an attractive interaction between electrons (Cooper pairs), the normal state of an otherwise free electron gas becomes unstable to the formation of a coherent many-body ground state.
Theories exist which explain such anomalies, and the nature of the gap as we will soon see is a vital property to be considered in any theory describing superconductivity in the high-T
musr.physics.ubc.ca /theses/Sonier/MSc/node12.html   (947 words)

  
 Superconductors
BCS theory says that at low enough temperatures, the electrons in a crystal lattice will behave cooperatively, a sea of electrons.
Pines and Scalapino's theory is not much different from the BCS theory -- in the new theory, electrons again pair up, but this time due to a different one of the four forces, the magnetic force.
Their theory says that in a superconductor, if two perpendicular currents are applied, the electron waves will cancel each other out, producing a net current of zero.
www.phy.duke.edu /~kolena/modern/superconductors.html   (1664 words)

  
 Leon Cooper, Cooper Pairs, and the BCS Theory
Leon Cooper, Cooper Pairs, and the BCS Theory
R. Schrieffer, for his studies on the theory of superconductivity which was completed while still in his 20s.
His concept of Cooper pairs forms the basis of the BCS theory.
www.osti.gov /accomplishments/cooper.html   (358 words)

  
 BCS theory
This theory was intended to describe superconductivity and critical magnetic field strengths in the superconductors that were known at that time.
BCS theory states that Superconductivity occurs through the formation of "Cooper" pairs: At low temperature, electrons starts to attract each other via lattice vibration (phonons) and form pairs, i.e.
However, BCS theory in itself is independent of the "glue" that causes this pairing.
www.physicsforums.com /showthread.php?t=11739   (2024 words)

  
 BCS Theory
This BCS theory prediction of Cooper pair interaction with the crystal lattice has been verified experimentally by the isotope effect.
That is, the critical temperature of a material depends on the mass of the nucleus of the atoms.
The BCS Theory did exactly what a physical theory should do: it explained properties already witnessed in experiment, and it predicted experimentally verifiable phenomena.
ffden-2.phys.uaf.edu /212_fall2003.web.dir/T.J_Barry/bcstheory.html   (622 words)

  
 [No title]
It is shown that the BCS Hamiltonian can be straightforwardly derived from the second quantization formalism of the general fermion Hamiltonian under the condition of zero total momentum, k + k’ = 0.
A reinterpretation of the BCS Hamiltonian in the particle-hole channel leads to an understanding consistent with the positive Hubbard model in the Coulombic framework.
The BCS Hamiltonian still works for low-Tc superconductors and can be explained and understood consistently with the positive Hubbard Hamiltonian that is widely believed to be suitable for high-Tc superconductors.
www.phys.subr.edu /conference/Sample.Abst.doc   (289 words)

  
 Physics Today July 2001
In the aftermath of the BCS theory came the discoveries of magnetic-flux quantization, the proximity effect, and--most prominently--the novelties of tunneling.
BCS theory predicted an energy gap in superconducting lead, but its effect on tunneling was uncertain.
He therefore spoke at the session about Anderson's pseudospin formulation of BCS theory (in which the angular orientation of the spins is a variable) and its relation to the phase of the F functions in Gor'kov's formulation of BCS theory.
www.physicstoday.org /pt/vol-54/iss-7/p46.html   (4120 words)

  
 The BCS Theory of Superconductivity, first edition, first printing
A significant step forward was taken around 1950 when it was found theoretically and experimentally that the mechanism for superconductivity had to do with the coupling of electrons to the vibrations of the crystal lattice.
The theory also predicted new effects and it stimulated an intensive activity in theoretical and experimental research, which opened up new areas for research.
The key ideas of the theory were announced in two short letters in two separate issues of The Physical Review before the full developed theory was published in December, 1957.
www.theworldsgreatbooks.com /bcs.htm   (415 words)

  
 The BCS Theory of Superconductivity, first edition, first printing
A significant step forward was taken around 1950 when it was found theoretically and experimentally that the mechanism for superconductivity had to do with the coupling of electrons to the vibrations of the crystal lattice.
One may as examples mention the use of the quantum mechanical tunnel phenomena to study superconductors, the discovery of magnetic flux quantization and the remarkable Josephson effects.
The key ideas of the theory were announced in two short letters in two separate issues of The Physical Review before the full developed theory was published in December, 1957.
www.manhattanrarebooks-science.com /bcs.htm   (415 words)

  
 BCS Theory   (Site not responding. Last check: 2007-10-26)
BCS theory explains the occurrence of superconductivity quantum mechanically through the interaction of electrons and phonons [
For this reason the number of scattering processes allowed to the electrons of a Cooper pair, and consequently the amount by which their total energy decreases, is sharply maximal when their centre of mass is stationary.
The BCS ground state contains as many Cooper pairs as can form with a negative potential energy of greater magnitude than the requisite kinetic energy increment.
musr.physics.ubc.ca /theses/Price/node9.html   (419 words)

  
 Graduate Courses   (Site not responding. Last check: 2007-10-26)
The phenomena of superconductivity, the Cooper pair problem, BCS theory, the electron-phonon interaction and the Eliashberg theory of strong coupling superconductors.
The physics of ocean waves and tides; theory of surface and internal waves, windwave spectra, theory and analysis of the astronomical tides, seiches and co-oscillations.
Abstract group theory, theory of group representations, physical applications of group theory to problems in condensed matter physics and atomic and molecular physics.
www.physics.mun.ca /MUNPhys/grad_brochure/courses.html   (854 words)

  
 Superconducting phase coherence in the presence of a pseudogap: relation to specific heat, tunneling and vortex core ...   (Site not responding. Last check: 2007-10-26)
The authors demonstrate how, using a natural generalization of BCS theory, superconducting phase coherence manifests itself in phase insensitive measurements-when there is a smooth evolution of the excitation gap Δ from above to below Tc.
A central parameter of our extended BCS theory is Δ2-Δsc2 which is a measure of the no. of bosonic pair excitations which have a non-zero net momentum.
Applying this theory we find that the Bose condensation of Cooper pairs, which is reflected in Δsc, leads to sharp peaks in the spectral function once T ≤ Tc.
mrsec.uchicago.edu /Publications/Levin/levin008.html   (306 words)

  
 f
Initially, physicists attempted to apply the BCS theory, and especially Cooper Pairs, to high-temperature superconductors, but most were quickly convinced that at least some modifications were necessary.
While no theory has produced a truly distinct symmetry, the elimination of s-wave symmetry, for example, would eliminate the theories which called for that, and the same with eliminating d-wave symmetry possibilities.
One of the foremost d-wave symmetrical theories is known as the spin-wave theory.
www.angelfire.com /in/thamizhavel/s.html   (4731 words)

  
 Superconductivity - BCS Theory
In 1957, Bardeen, Cooper and Schrieffer (BCS) proposed a theory that explained the microscopic origins of superconductivity, and could quantitatively predict the properties of superconductors.
Mathematically, BCS theory is complex, but relies on an earlier 'discovery' by Cooper (1956), who showed that the ground state of a material is unstable with respect to pairs of 'bound' electrons.
The formation of Cooper pairs is supported by the fact that BCS and the Ginzburg-Landau theories predict the charge and mass of the supercurrent 'particle' to be 2e and 2M
www.chm.bris.ac.uk /webprojects2000/igrant/bcstheory.html   (457 words)

  
 Superconductor Terms
The theory asserts that, as electrons pass through a crystal lattice, the lattice deforms inward towards the electrons generating sound packets known as "phonons".
According to BCS theory, the formula for determining the energy gap (in meV) is E
Since electron-pairing is universally agreed to be the method by which superconductivity occurs, this is the amount of energy required to disrupt the superconducting state.
www.superconductors.org /terms.htm   (4413 words)

  
 Re: How can electrons in a superconductive material bind themselves together...
The theoretical understanding of superconductivity was advanced in 1957 by three American physicists -John Bardeen (who also worked on developing the first Solid State transistor), Leon Cooper, and John Schrieffer-, through their Theory of Superconductivity, known as the BCS Theory.
BCS Theory is extremely complicated and involves many advanced Solid State and Quantum Mechanics topics (Statistical Quantum Mechanics, Quantum Lattice Vibrations, Fermion and Boson Dynamics, Second Quantization...).
According to BCS Theory in a superconducting metal electrons seem to be in bonded pairs, linked by some attractive force between them.
www.madsci.org /posts/archives/2000-12/976031589.Ph.r.html   (541 words)

  
 EPG603: Effects of Broadening on BCS Theory...   (Site not responding. Last check: 2007-10-26)
Effects of Broadening on BCS Theory in the Presence of Van Hove Singularities
There have been recent suggestions that high-Tc superconductivity can be understood in terms of conventional BCS theory if there is a logarithmic Van Hove singularity in the electron density of states near the Fermi energy as suggested by band theory.
We consider the effects of broadening of the singularity on theories of this type.
physics.nist.gov /Divisions/Div841/Gp3/Pubs/abstract/epg603.html   (86 words)

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