What is the explanation of bcs theory for the zero. In a theoretical model that has since been called bcs, after their initials, they proposed the following explanation. 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. The bcs theory is based on a weak coupling approximation, i. Much of the physics involved in the bcs theory can be discussed in the context of a simple quantum mechanics problem. Superconductivity article about superconductivity by the. We will then calculate and study interesting quantities of the su. 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. What is the explanation of bcs theory for the zero resistance. An intuitive description of superconductivity is sufficient for public and nontechnical uses. The properties of type i superconductors were modeled successfully by the efforts of john bardeen, leon cooper, and robert. High temperature superconductivity articles inference.
The bcs theory predicts a bandgap of where t c is the critical temperature for the superconductor. Bardeencooperschrieffer bcs theory of superconductivity. 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 explains the phenomenon in which a current of electron pairs. The microscopic theory of superconductivity by bardeen, cooper and schrieffer bcs is considered one of the most successful theories in condensed matter physics. 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. 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. Thus, we recover a result similar to our simplified analysis of the schrodinger equation. 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. The bcs theory of superconductivity has successfully described the measured properties of type i superconductors.
Bcs theory was developed in 1957 by john bardeen, leon cooper, and john schrieffer in order to explain why superconductivity occurs. 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. Most high tc superconductors belong to typeii ones. Superconductivity happens when electrons work together in cooper pairs. This idea was further developed as a natural explanation of superconductivity by schafroth. This result had a simple explanation within the then recent bcs theory of superconductivity. 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. Bcs theory of superconductivity hyperphysics concepts. In ordinary metal superconductors the coherence length xi is large, and a simple mean field approach, such as bcs, is thereby justified. May 30, 2019 the basic theory of superconductivity, bcs theory, earned the scientistsjohn bardeen, leon cooper, and john schriefferthe 1972 nobel prize in physics.
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. 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. Bcs theory starts from the assumption that there is some attraction between electrons, which can overcome the coulomb repulsion. Maurice rice, in contemporary concepts of condensed matter science, 2011. Generalization of bcs theory to short coherence length. For this work, the authors were awarded the nobel prize in 1972. This bcs theory explained the superconducting current as a superfluid of cooper pairs, pairs of electrons interacting through the exchange of phonons. 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. We give a short, simplified argument of for this fact. The theory of electromagnetism has a symmetry, called mathu1math gauge symmetry, which forces the phot. In ordinary metal superconductors the coherence length is large, and a simple mean.
Why bcs theory of superconductivity cant explain the. 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. The bcs theory is, in its simplest form, actually contradictory to our crude. Bcs theory of superconductivity is one of the greatest, if not the greatest, achievement of modern condensed matter physics. For a material to behave as a superconductor, low temperatures are required. In fact, many incorrect theories of superconductivity were advanced before the bcs theory was proposed. We will look at features of superconductors before the discovery of the bcs theory, and examine the assumptions and methods used to develop the theory.
Historically, this approach has been very successful. Why does bcs theory fail to explain superconductivity at. Superconductivity was not sufficiently explained until 1957 when john bardeen and. 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 of superconductivity an intuitive description of superconductivity is sufficient for public and nontechnical uses. Want to understand how superconductors but dont have a quantum mechanics degree. Superconductive article about superconductive by the free. In particular, you saw that given some empirical results, many additional predictions can be made using the ginzburglandau formalism. However, ultimately, a more rigorous mathematically based explanation must be formulated.
Oct 09, 2014 i know that bcs theory cannot explain high tc superconductor. The simplest explanation for meissner effect is spontaneous symmetry breaking yes. Jul 22, 2008 bcs theory was developed in 1957 by john bardeen, leon cooper, and john schrieffer in order to explain why superconductivity occurs. This theory is remarkable enough that it is interesting to look at the chain of ideas which led to it.
The main point of the bcs theory is that the attractive electronelectron. Consider two electrons that interact with each other via an attractive potential. It envisions resistancefree conduction of coupled pairs of electrons called cooper pairs. Click download or read online button to get on the theory of superconductivity book now.
The energy gap is related to the coherence length for the superconductor, one of the two characteristic lengths associated with superconductivity. I doubt any explanation of the meissner effect within todays formulation of the s. 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. A portion of the 1973 nobel prize in physics went to brian josephson, also for work with superconductivity. Superconductivity was discovered in 1911 by onnes, who was studying the resistivity of solid mercury at cryogenic temperatures using the recentlydiscovered liquid helium as a refrigerant.
Eremin, maxplanck institut fur physik komplexer systeme, dresden, germany. The theory also implies that the electronphonon interaction, assumed in bcs theory to be the cause of superconductivity, is in fact irrelevant to superconductivity. There are a number of practical applications of superconductivity. It explains the phenomenon in which a current of electron pairs flows without resistance in certain materials at low temperatures. 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. Superconductive article about superconductive by the. 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. Much of the physics involved in the bcs theory can be discussed in the context of a simple quantum mechanics. Bcs theory physics britannica encyclopedia britannica. 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. This theory explained resistanceless transport and the meissner effect, and allowed the first theoretical predictions for superconductivity to be made. The basic theory of superconductivity, bcs theory, earned the scientistsjohn bardeen, leon cooper, and john schriefferthe 1972 nobel prize in physics. Superconductor simple english wikipedia, the free encyclopedia.
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. The theory describes superconductivity as a microscopic effect caused by a condensation of cooper pairs. A theory of superconductivity formulated by john bardeen, leon cooper, and robert schrieffer. This can happen, so the theory says, when a single. In 1957, bardeen, cooper and schrieffer bcs proposed a theory that explained the microscopic origins of superconductivity, and could quantitatively predict. 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. What types of mathematics are required to fully understand. How is the meissner effect explained by the bcs theory. In fact, many incorrect theories of superconductivity. 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.
Here is a simplified explanation of the bcs theory to. This site is like a library, use search box in the widget to get ebook that you want. Bcs theory is the most commonly accepted explanation for superconductivity. 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. 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, in physics, a comprehensive theory developed in 1957 by the american physicists john bardeen, leon n.
The bcs theory still stands as the basic explanation of superconductivity, even though extensive theoretical work has embellished it. The complete microscopic theory of superconductivity was finally proposed in 1957 by bardeen, cooper and schrieffer. Bcs states that electrons move through crystalline lattices in pairs due to vibrations in the lattice and the spacing of electrons within it. Called the bcs theory in honor of its three discovers, it explains that materials suddenly become superb conductors when the electrons inside them join forces to make what are called cooper pairs or bcs pairs. It has been suggested that a quantum critical point qcp might form the basis for high t c superconductivity.
Suppose an electron approaches a positive ion core. Tutorial 4 the bcs theory of superconductivity june 1, 2015 in the lectures you saw a phenomenological analysis of superconductors. Superconductivity is the ability of certain materials to conduct electric current with practically zero resistance. 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 to predict high hc2 and low hc1 for typeii conventional superconductor in bcs theory. 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. Schrieffer their surname initials providing the designation bcs to explain the behaviour of superconducting materials. 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. Superconductivity was simultaneously explained by nikolay bogolyubov, by means of the bogoliubov transformations.
This capacity produces interesting and potentially useful effects. Thesecooperpairsformthenacoherentmacroscopicgroundstate,whichdisplaysagapped spectrumandperfectdiamagnetism. Can bcs theory explain typeii conventional superconductor. Here is a simplified explanation of the bcs theory to help you, sing a clear explanation with animations, i help. Explanation as to how superconductivity works physics forums. 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. The bardeencooperschrieffer bcs theory describes how the electrons in a conductor form the ordered superconducting state. 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. 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. Explanation consider the 1st electron with wave vector k distorts the lattice, there by emitting a phonons of wave vector q.
1129 411 987 972 1214 133 844 1134 471 478 679 1303 495 965 729 935 258 1572 713 582 1060 1113 526 1547 569 78 1185 41 404 499 745 1029 1470 1011