Explanation as to how superconductivity works physics forums. Bcs theory of superconductivity hyperphysics concepts. What is the explanation of bcs theory for the zero resistance. What is the explanation of bcs theory for the zero.
Historically these were the first superconducting materials studied, and based on the experimental knowledge gained from them the bcs theory of superconductivity was developed in 1957. How to predict high hc2 and low hc1 for typeii conventional superconductor in bcs theory. The bcs theory of superconductivity has successfully described the measured properties of type i superconductors. The bcs theory is based on a weak coupling approximation, i. Historically, this approach has been very successful. Consider two electrons that interact with each other via an attractive potential. The theory also implies that the electronphonon interaction, assumed in bcs theory to be the cause of superconductivity, is in fact irrelevant to superconductivity. Eremin, maxplanck institut fur physik komplexer systeme, dresden, germany. The nobel prize in physics 1972was awardedjointly to john bardeen, leon neil cooper and john robert schriefferfor their jointly developedtheory of superconductivity, usually called the bcstheory. Oct 05, 2016 bcs theory or bardeencooperschrieffer theory named after john bardeen, leon cooper, and john robert schrieffer is the first microscopic theory of superconductivity since its discovery in 1911. It envisions resistancefree conduction of coupled pairs of electrons called cooper pairs. While bcs theorys predictions like isotope effect are excellent, i could never completely understand what is the origin of zero resistance in superconductors according to bcs theory. This bcs theory explained the superconducting current as a superfluid of cooper pairs, pairs of electrons interacting through the exchange of phonons.
A key conceptual element in this theory is the pairing of electrons close to the fermi level into cooper pairs through interaction with the crystal lattice. Thus, we recover a result similar to our simplified analysis of the schrodinger equation. Oct 09, 2014 i know that bcs theory cannot explain high tc superconductor. Within the bcs theory, the electronphonon interaction is the source of the attraction that binds two electrons into a paired state, generally referred to as cooper pairs. Bcs theory of superconductivity is one of the greatest, if not the greatest, achievement of modern condensed matter physics. Bardeencooperschrieffer bcs theory of superconductivity.
The theory describes superconductivity as a microscopic effect caused by a condensation of cooper pairs. A good starting point would be to learn about bcs bardeencooperschrieffer theory, which explains superconductivity in conventional critical temperature approximately tc jan 15, 2017 want to understand how superconductors but dont have a quantum mechanics degree. May 30, 2019 the basic theory of superconductivity, bcs theory, earned the scientistsjohn bardeen, leon cooper, and john schriefferthe 1972 nobel prize in physics. The bcs theory predicts a bandgap of where t c is the critical temperature for the superconductor. Bcs theory of superconductivity an intuitive description of superconductivity is sufficient for public and nontechnical uses. Superconductivity and bcs theory introduction electronphonon interaction, cooper pairs bcs wave function, energy gap and quasiparticle states predictions of the bcs theory limits of the bcs gap equation. Thesecooperpairsformthenacoherentmacroscopicgroundstate,whichdisplaysagapped spectrumandperfectdiamagnetism. Bcs theory physics britannica encyclopedia britannica. In ordinary metal superconductors the coherence length is large, and a simple mean. This capacity produces interesting and potentially useful effects. Jul 22, 2008 bcs theory was developed in 1957 by john bardeen, leon cooper, and john schrieffer in order to explain why superconductivity occurs. Superconductivity article about superconductivity by the.
This can happen, so the theory says, when a single negatively charged electron slightly distorts the lattice of atoms in the superconductor, drawing toward it a small. It has been suggested that a quantum critical point qcp might form the basis for high t c superconductivity. In ordinary metal superconductors the coherence length xi is large, and a simple mean field approach, such as bcs, is thereby justified. It explains the phenomenon in which a current of electron pairs. In particular, you saw that given some empirical results, many additional predictions can be made using the ginzburglandau formalism. Bcs theory describes the formation of electron pairs, or cooper pairs, moving through the crystal lattice unimpeded and bypassing the obstacles in the crystal lattice which were responsible for electrical resistance. Why does bcs theory fail to explain superconductivity at high. Suppose an electron approaches a positive ion core. High temperature superconductivity articles inference. Most high tc superconductors belong to typeii ones. Superconductive article about superconductive by the free.
Want to understand how superconductors but dont have a quantum mechanics degree. The main point of the bcs theory is that the attractive electronelectron interaction mediated by the phonons gives rise to cooper pairs, i. Bcs theory was developed in 1957 by john bardeen, leon cooper, and john schrieffer in order to explain why superconductivity occurs. Superconductivity happens when electrons work together in cooper pairs. Click download or read online button to get on the theory of superconductivity book now. Why does bcs theory fail to explain superconductivity at. On the theory of superconductivity download ebook pdf. Superconductivity was simultaneously explained by nikolay bogolyubov, by means of the bogoliubov transformations. Bcs theory of superconductivity the properties of type i superconductors were modeled successfully by the efforts of john bardeen, leon cooper, and robert schrieffer in what is commonly called the bcs theory. Bcs theory or bardeencooperschrieffer theory named after john bardeen, leon cooper, and john robert schrieffer is the first microscopic theory of superconductivity since heike kamerlingh onness 1911 discovery.
How is the meissner effect explained by the bcs theory. In 1957, bardeen, cooper and schrieffer bcs proposed a theory that explained the microscopic origins of superconductivity, and could quantitatively predict. Bcs theory applies directly to superconductors such as nb3ge tc 23k in which the electrons are bound together by their interaction with the vibrations of the underlying lattice. Prior to this, there was ginzburglandau theory, suggested in 1950, which was a macroscopic theory.
The bcs theory has proven inadequate to fully explain cuprate superconductivity and it seems that a satisfactory microscopic explanation will require an entirely different set of ideas. One reason that superconductivity remained unexplained for so long is the smallness of the energy changes that accompany the transition between normal and superconducting states. An intuitive description of superconductivity is sufficient for public and nontechnical uses. Bcs theory starts from the assumption that there is some attraction between electrons, which can overcome the coulomb repulsion. It explains the phenomenon in which a current of electron pairs flows without resistance in certain materials at low temperatures. This site is like a library, use search box in the widget to get ebook that you want. Bcs theory is unable to predict new superconductors because it assumes that superconductivity is associated with the electronphonon interaction. The basic theory of superconductivity, bcs theory, earned the scientistsjohn bardeen, leon cooper, and john schriefferthe 1972 nobel prize in physics.
The simplest explanation for meissner effect is spontaneous symmetry breaking yes. However, ultimately, a more rigorous mathematically based explanation must be formulated. We give a short, simplified argument of for this fact. The main point of the bcs theory is that the attractive electronelectron. Instead, according to the accepted theory of superconductivity since 1957, bcs theory, the lifting of the magnet in the case of the superconductor meissner effect is not explained by the same physics. The complete microscopic theory of superconductivity was finally proposed in 1957 by bardeen, cooper and schrieffer. Schrieffer theory of superconductivity addisonwesley.
I doubt any explanation of the meissner effect within todays formulation of the s. Much of the physics involved in the bcs theory can be discussed in the context of a simple quantum mechanics. The energy gap is related to the coherence length for the superconductor, one of the two characteristic lengths associated with superconductivity. Why bcs theory of superconductivity cant explain the. In fact, many incorrect theories of superconductivity. Quite the contrary, the same physics would predict that the magnetic field lines stay put, frozen, inside the superconductor which is also a. Bcs states that electrons move through crystalline lattices in pairs due to vibrations in the lattice and the spacing of electrons within it. Superconductivity classical alternatives to modern theory. This theory explained resistanceless transport and the meissner effect, and allowed the first theoretical predictions for superconductivity to be made. If the interaction between a conduction electron spin s and the 4f local moment spin on the impurity atom s is supposed of the form h int 2j int ss 2g 1. There are a number of practical applications of superconductivity.
In a theoretical model that has since been called bcs, after their initials, they proposed the following explanation. For a material to behave as a superconductor, low temperatures are required. The theory of electromagnetism has a symmetry, called mathu1math gauge symmetry, which forces the phot. Bcs theory finite temperatures the model hamiltonian bogoliubovvalatintransformation calculation of the condensation energy bcs theory having seen that the fermi sea is unstable against the formation of a bound cooper pair when the net interaction is attractive, we must then expect pairs to condense until an equilibrium point is reached. Bcs theory fails to explain high temperature superconductivity because electronphonon coupling cannot be made strong enough and more importantly because the hightc superconductors lack a fermi surface just above tc. Aug 18, 2010 bcs theory showed that the basic interaction responsible for superconductivity appears to be that of a pair of electrons by means of an interchange of virtual phonons. The bardeencooperschrieffer bcs theory describes how the electrons in a conductor form the ordered superconducting state. This work offers a simple model which explains the behavior of the superconducting gap based on bcs theory, and reproduces most effects seen in.
Tutorial 4 the bcs theory of superconductivity june 1, 2015 in the lectures you saw a phenomenological analysis of superconductors. Maurice rice, in contemporary concepts of condensed matter science, 2011. This theory is remarkable enough that it is interesting to look at the chain of ideas which led to it. The properties of type i superconductors were modeled successfully by the efforts of john bardeen, leon cooper, and robert. Jan 25, 20 also, i should warn you that even though the theories of superconductivity bcs theory, landauginzburg etc are relatively simple compared to many other topics in condensed matter, it is still not exactly easy and you will struggle with the theory unless youve done a couple of courses in quantum mechanics and statistical physics.
Can bcs theory explain typeii conventional superconductor. This idea was further developed as a natural explanation of superconductivity by schafroth. Apr 01, 2017 the wavefunction for the bcs state that bob schrieffer discovered on a train to long island while he was a graduate student astonishingly has an indefinite number of electrons. A portion of the 1973 nobel prize in physics went to brian josephson, also for work with superconductivity. For this work, the authors were awarded the nobel prize in 1972. Bcs theory is the most commonly accepted explanation for superconductivity. Schrieffer their surname initials providing the designation bcs to explain the behaviour of superconducting materials. Bcs theory, in physics, a comprehensive theory developed in 1957 by the american physicists john bardeen, leon n. In most materials in low temperature superconductors, this attraction is brought about indirectly by the coupling of electrons to the crystal lattice as explained above. Here is a simplified explanation of the bcs theory to help you, sing a clear explanation with animations, i help.
However, this theory only explained experimental observations it did not allow the microscopic origins of the superconducting properties to be identified. The microscopic theory of superconductivity by bardeen, cooper and schrieffer bcs is considered one of the most successful theories in condensed matter physics. We will then calculate and study interesting quantities of the su. Bcs theory or bardeencooperschrieffer theory named after john bardeen, leon cooper, and john robert schrieffer is the first microscopic theory of superconductivity since its discovery in 1911. Here is a simplified explanation of the bcs theory to. Superconductor simple english wikipedia, the free encyclopedia. Superconductivity in the elements, alloys and simple. Superconductive article about superconductive by the. 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. The theory, which has been able to describe the behavior of type i superconductors to a high degree of accuracy, was developed by john bardeen, leon cooper, and robert schrieffer in 1957. Explanation consider the 1st electron with wave vector k distorts the lattice, there by emitting a phonons of wave vector q. In fact, many incorrect theories of superconductivity were advanced before the bcs theory was proposed. Much of the physics involved in the bcs theory can be discussed in the context of a simple quantum mechanics problem. The bcs theory still stands as the basic explanation of superconductivity, even though extensive theoretical work has embellished it.
Superconductivity is the ability of certain materials to conduct electric current with practically zero resistance. A theory of superconductivity formulated by john bardeen, leon cooper, and robert schrieffer. This can happen, so the theory says, when a single. While bcs theory s predictions like isotope effect are excellent, i could never completely understand what is the origin of zero resistance in superconductors according to bcs theory. In 1957, more than 40 years after the discovery of superconductivity, three physicists, bardeen, cooper and schrieffer, finally found the correct explanation to superconductivity in metals. Because of the pauli exclusion principle these pairs operate together at a low level of energy that inhibits the kind of collisions that lead to resistance.
924 1021 700 210 498 703 353 609 956 1086 748 135 1365 412 1197 1100 669 85 507 434 354 741 411 444 17 1281 1332 770 1068 1494 1132 403 595 1246 7 1366 414 228 1287 301 103 1117 223