These two electrons are paired to form a single system. Discovery of superconductivity superconductivity was first discovered in 1911 by the dutch physicist,heike kammerlingh onnes. The central feature of the bcs theory is that two electrons in the superconductor are able to form a bound pair called a cooper pair if they somehow experience an attractive interaction between. Although cooper pairing is a quantum effect, the reason for the pairing. But electrons are fermions, and we cannot have more than 1 electron on quantum state, so there is. Moreover, superconductivity is not an isolated phenomenon. These two electrons form a cooper pair and is known as cooper electron. Standard superconductors consist of a condensate of paired electrons, called cooper pairs. Although cooper pairing is a quantum effect, the reason for the pairing can be seen from a simplified classical explanation. Superconductivity was discovered by kamerlinghonnes in 1911, when he was studying the transport. As showed by cooper, an attraction between electrons in a metal can cause a paired state of electrons to have a lower energy than the fermi energy, which implies that the pair is bound. In condensed matter physics, a cooper pair or bcs pair is a pair of electrons or other fermions bound together at low temperatures in a certain manner first described in 1956 by american physicist leon cooper. Superconductivity and physics of nanomaterials prepared by p g logan, dept of physics, sistk, puttur.
Superconductivity by bardeen, cooper, and schrie er or tinkhams introduction to superconductivity. Twoelectron and twohole cooper pairs in superconductivity. My first introduction to superconductivity came in the 1930s and i greatly profited from reading david shoenbergs little book on superconductivity, i which gave an excellent summary of the experimental findings and of the phenomenological theories that had been developed. The cooper pairs do not have spin 12 and therefore do not follow paulis principle 1 electron per state. This does not happen, and therefore there is no scattering of cooper pairs and therefore the conductivity is infinite.
Quantum modes of superconducting transmission lines see r. Kamerlingh onnes made the first discovery 1 of the phenomenon in 1911 in mercury hg as shown in fig. This pair condensation is the basis for the bcs theory of superconductivity. A cooper pair, is a pair of electrons with a phononic interaction. Binding energy of cooper pair is largest when all are in same state. Bcs theory of superconductivity john bardeen leon neil cooper john robert schrieffer of the prize of the prize of the prize usa usa usa university of illinois urbana, il, usa brown university providence, ri, usa university of pennsylvania philadelphia, pa, usa b.
Oct 28, 2014 the theory states that the supercurrent in a superconductor is carried by many million bound electron pairs, called cooper pairs. Superconductivity requires electrons to form cooper pairs, in which the spins point oppositely to form a singlet state. Superconductivity experiments experimental physics i. A pair of weakly bound electrons in a superconductor is called cooper pair. Bcs state intheprevioussectionwesawthattwoelectronsnearthefermilevelareunstabletowardstheformation of a cooper pair for an arbitrarily small attractive interaction. According to a book on superconductivity that cooper showed me, many physicists were even disappointed that superconductivity should, on the atomistic scale, be revealed as nothing more than a footling small interaction between electrons and lattice vibrations. Thus, the transition from the normal metal state to the super conducting state must be a phase transition.
Phonon mediated attractive interaction and the cooper pairs. Onnes, felt that a cold wires resistance would dissipate. Cooper john robert schrieffer of the prize of the prize of the prize usa usa usa university of illinois urbana, il, usa brown university providence, ri, usa university of pennsylvania philadelphia, pa, usa b. In the weak coupling limit we can answer this question. Although cooper pairing is a quantum effect, the reason for the pairing can be seen from a simplified classical. 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. The cooper pair is generally analyzed in momentum space, but its realspace structure also follows directly from the bcs theory. Cooper pairs to understand the mechanism of cooper pair formation, let us consider the distribution of electrons in metals as given by the fermidirac distribution function. Lecture notes on superconductivity a work in progress daniel arovas congjun wu department of physics university of california, san diego june 23, 2019.
Superconductivity by bardeen, cooper, and schrieffer or tinkhams introduction to superconductivity. Superconductivity, third edition is an encyclopedic treatment of all aspects of the subject, from classic materials to fullerenes. The energy of the electron interaction is quite weak and the pairs can be easily broken up by thermal energy this is why superconductivity usually occurs at very low temperature. The central feature of the bcs theory is that two electrons in the superconductor are able to form a bound pair called a cooper pair if they somehow experience an attractive interaction between them. Tavkhelidze ilia state university, 35 cholokashvili avenue, tbilisi 0162, georgia avtandil. This video lecture will explain the bcs theory of superconductivity. Since that time, superconductivity has been found to occur in many metallic elements and intermetallic compounds. The energy of the pairing interaction is quite weak, of the order of 10. In the future this novel comprehension of how super conductivity works may give a guideline to develop improved superconductors especially in the hightempera ture superconductivity area. The reader will master london theory and the pippard equations, and go on to understand type i and type ii superconductors their thermodynamics, magnetic properties, vortex dynamics, current transport, cooper pairs and the results. The cooper pair state is responsible for superconductivity, as described in the bcs theory developed by john bardeen, leon cooper, and john schrieffer for which they shared the 1972 nobel prize. Free superconductivity books download ebooks online. Cooper had discovered that electrons in a superconductor are grouped in pairs, now called cooper pairs, and that the motions of all of the cooper pairs within a single superconductor are correlated.
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. Mechanism of cooper pairing in layered high temperature superconductors a. The tunneling of cooper pairs through an insulating junction between two superconductors the dc josephson e ect is demonstrated, and the magnitude of the uxoid is measured by observation of the e ect of a magnetic eld on the josephson current. Brief introduction to superconductivity pdf 69p covered topics are discovery and first insights, the physics of the cooper pairs, bcs theory of superconductivity, characteristics of the superconducting state, the strong coupling theory, hightc superconducting materials, crystal structures, superconducting properties, models on the mechanism. The formation of cooper pairs due to the interaction of electrons with the crystal lattice, along with their condensation to act as composite bosons, is thus believed to be the reason for superconductivity. The bcs theory revolutionized our understanding of this fascinating phenomenon. So, in this collective state, they can all move together. Page 5 dc josephson effect without any applied voltage across the junction due to tunneling of cooper pairs, a small direct super current dc flows across the junction. Because electrons are fermions possess halfintegral spins, they obey the pauli exclusion principle and thus cannot occupy the same quantum state.
What is the relation of cooper pair with superconductivity. Cooper pairs and the bcs theory of superconductivity. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. Cooper pair and the bcs theory superconductivity and superfluid are very similar no resistivity vs no viscosity, which implies that the fundamental physics may be similar. The classic form of superconductivity was finally explained by the nobelwinning bcs bardeen cooper schrieffer theory in the 1950s, as a superfluid of electron pairs interacting via the. Superconducting state generated by cooper pairs bound by. For this work, the authors were awarded the nobel prize in 1972. A cooper pair can be basically regarded as wave packed. He also gave what may be the first indication of an energy gap when he stated that the electrons be coupled by some form of interaction in such a way that the. The tunneling of cooper pairs through an insulating junction between two superconductors the dc josephson effect is demonstrated, and the magnitude of the fluxoid is measured by observation of the effect of a magnetic field on the josephson current. This book proposes a thorough introduction for a varied audience.
A phase transition is accompanied by an instability of the normal state. The behavior of superconductors suggests that electron pairs are coupling over a range of hundreds of nanometers, three orders of magnitude larger than the lattice spacing. The specific heat of a superconductor cs and and normal metal cn. When two superconductors are in contact via a normal metal, the pairs must convert to singleparticle states to traverse between superconductors. Both have layered structure and non planar geometry of the layers.
Called cooper pairs, these coupled electrons can take the character of a boson and condense into the ground state. Leon cooper of bardeen, cooper and schrieffer discovered the solution to this problem, showing that in order to form a condensate, electrons must form pairs first. Thermal conductivity is a powerful tool that can be used to indirectly probe the symmetry of the sc order parameter18. These two electrons are attracted by the exchange of phonons. The discussion begins, after a brief introduction, with cooper pairs, and then the bardeen cooper schrieffer bcs order parameter and the bcs hamiltonian are examined. The electrons are phase locked and it is a boson allowing it to occupy the same state as other cooper pairs. Super conductors and cooper pair free download as powerpoint presentation. The complete microscopic theory of superconductivity was finally proposed in 1957 by bardeen, cooper and schrieffer. A description of superconductivity in a little more detail than you need at a level to explain the basic concepts of a quantum mechnical phenomenon. In the cooper pairs of conventional superconductors, the wave functions are as symmetrical as possible. However, inside a typeii superconductor is one situation where the magnetic flux really is divided into discrete, separate lines. Super conductors and cooper pair superconductivity. In conventional superconductors, the creation of electron pairs and the formation of the condensate happen instantaneously. The electronelectron coupling results in electron pairing formation of cooper pairs.
Key to the formation of cooper pairs is the existence of a welldefined. This bcs theory explained the superconducting current as a superfluid of cooper pairs, pairs of electrons interacting through the exchange of phonons. The space occupied by one pair contains many other pairs, and there is thus a complex interdependence of the occupancy of the pair states. Bardeen, cooper and schrie er bcstheory, 1957 3,4, the electrons in the super conducting electron gas are correlated in pairs cooper pairs whose binding energy despite the low entropy stabilizes the superconducting state with regard to the normal nonsuperconducting state. Super conductivity part 1 engineering physics 1 lectures.
Superconductivity is widely regarded as one of the great scientific discoveries of the 20th century. Superconductivity is a unique and powerful phenomenon of nature. We revisit the generalized boseeinstein condensation gbec theory which addresses a ternary bosonfermion gas including twohole cooper pairs 2hcps as an essential component in superconductivity. Thus, we expect that the manybody electronicsystemwillbeunstabletowardstheformationofanewgroundstate,wherethesecooperpairs proliferate. Kadin princeton junction, new jersey 08550, usa october 11, 2005 abstract.
The cooper pair state is responsible for superconductivity, as. Super conductor are the material having almost zero resistivity and behave as diamagnetic below the super conducting transition temperature. The effective net attraction between the normally repulsive electrons produces a pair binding energy on the order of millielectron volts, enough to keep. This creates a band gap below the fermi energy and allows resistancefree flow through a material. Because condensed cooper pairs share the same quantum mechanical state, and therefore cannot carry entropy, a measurement of thermal conductivity in a superconductor can probe the leftover remnants of uncondensed quasiparticle. This was the beginning of the era of unconventional superconductivity, condensates of cooper pairs of lower symmetry, in contrast to the conventional superconductors with the most symmetric cooper pairs. Preparatory questions please visit the superconductivity chapter on the 8. These two electrons together form a cooper pair and is known as cooper electron.
The transport behavior of these pairs at junctions can produce exotic effects that are of fundamental and practical interest. This was the beginning of the era of unconventional superconductivity, condensates of cooper pairs of lower symmetry, in contrast to the conventional superconductorswith the most symmetriccooper pairs. We can obtain the superconducting order parameter of the hubbard model in the limit of small u, that is given by 6266 2 2 exp, xu 1 where u is the strength of the onsite coulomb. Pdf a possible fundamental theory of cooper pair formation in. Mar 05, 2012 a description of superconductivity in a little more detail than you need at a level to explain the basic concepts of a quantum mechnical phenomenon. Cooper pairs bcs theory two electrons fermions can interact due to the presence of a crystal lattice and form a bosonic pair these bosonic pairs condense into one common ground state wikipedia. A microscopic theory of superconductivity was developed in 1957 by john bardeen, leon cooper and j. Also, since cooper pairs overlap, they become entangled and act as one big group of currentcarrying particles. Superconductivity an overview sciencedirect topics. The tremendous efforts to unveil high temperature superconductivity htsc have been devoted to the search of the mechanism underlying cooper pairs which. Mar 08, 2012 superconductivity and its applications 1. In a high temperature superconductor hts materials, the cooper pairs are carriers of the superconducting.
So only at low temperatures, are a significant number of the electrons in a metal in cooper pairs. Superconductivity is a phenomenon in which the resistance of the material to the electric current flow is zero. Lecture notes on superconductivity a work in progress. A possible structure model of the cpf in all superconducting materials. Super conductivity general propertiesobservations regarding applications 2. It is based on the assumption that the supercurrent is not carried by single electrons but rather by pairs of. Electrons in a cooper pair have opposite spins hence cooper pair has zero spin i.
Bcs theory of superconductivity hyperphysics concepts. The cooper problem is a simplistic microscopic account of how superconductivity can arise. Cooper pairs do not collide w ith their peers a nd are not. Introduction to quantum mechanics of superconducting. Cooper and schrieffer or bcs in 1957, provides the better quantum explanation of superconductivity and account very well for all the properties exhibited by the superconductors. 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.
Nearly a century after its first discovery, its full commercial potential is. However, the cooper pair is coupled to a large number of other cooper pairs and so the whole collective of cooper pairs would have to be involved in scattering at once. The size of a cooper pair is given by the coherence length which is typically a though it can be as small as 30a in the copper oxides. And third, in real superconductors, the density of electrons is such that many cooper pairs typically, of order millions are present on the scale of the. A cooper pair is a weak electronelectron bound pair medi1. This suggested that there would be a steady decrease in electrical resistance, allowing for better conduction of electricity. Mechanism of cooperpairing in layered high temperature. In a super conductor if the transition temperature is high ie. An important concept from that theory is cooper pairs, which are formed by electrons. In conventional superconductors, this attraction is due to the electron phonon interaction.
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