The theory describes superconductivity as a microscopic effect caused by a condensation of cooper pairs. Topology and geometry for physics, the fundamentals of density functional theory, the particle world of condensed matter, theory of superconductivity. Eremin, mpipks first truly microscopic theory of superconductivity. Here is a simplified explanation of the bcs theory to help you, sing a clear explanation with animations, i. Theory of superconductivity advanced books classics. Want to understand how superconductors but dont have a quantum mechanics degree. 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.
I outline an alternative to conventional bcs theory proposed to apply to all superconductors, conventional. Their theory in nonmathematical terms can be summarized as follows. Superconductors abruptly lose all resistance to the flow of an electric current when they are cooled to temperatures near absolute zero. A qualitative discussion of a successful theory of superconductivity was given by bardeen, copper and schrieffer, known as bcs theory after the initials of their names. Thesecooperpairsformthenacoherentmacroscopicgroundstate,whichdisplaysagapped spectrumandperfectdiamagnetism. We will mostly focus on conventional superconductors, where the cooper pairs. 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 hyperphysics concepts. Pdf mechanism of high temperature superconductivity. The remaining four chapters are devoted to the simplest phenomenological weak coupling theory of superconductivity on a microscopic level, the bcs theory, which provided the. Although the theory is beyond the scope of this chapter, a short summary of the theory is provided here. Called cooper pairs, these coupled electrons can take the character of a boson and condense into the ground state. These lectures attempt at a concise description of what has been achieved so far in this direction. A microscopic theory of superconductivity was developed in 1957 by john bardeen, leon cooper and j.
Hole superconductivity the theory of hole superconductivity also known in some circles as the holistic theory of superconductivity asserts that superconductivity can only occur when hole carriers exist in the normal state of a metal. 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. In the case of a weak link between two superconductors, current. For the spin singlet state and swave symmetry a subsititon of the trial wave function in schrodinger equation 2, 1 2 e. 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. This pair condensation is the basis for the bcs theory of superconductivity.
Around 1960 gorkov 10 showed that the phenomenological ginzburglandau theory is a limiting case of the bcs theory. Bcs theory \ bcs bardeencooperschrie ertheoryisessentiallyjusthartreefocktheorylec. Free superconductivity books download ebooks online. The measured bandgap in type i superconductors is one of the pieces of experimental evidence which supports the 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. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a. The author proposed, for the first time, the change of. Bardeencooperschrieffer bcs theory of superconductivity. Electronic structure, bcs beschreibung des supraleitenden zustands. The aim of bcs theory is to provide a satisfactory explanation to the superconductivity of type i superconductors. The second essential observation was that superconductors not only prevent a magnetic. Due to this interaction, the electrons form bound pairs.
Pdf bcs theory for finite size superconductors juan. The groundstate wave function of a superconductor is formed by. 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. Prior to this, there was ginzburglandau theory, suggested in 1950, which was a macroscopic theory. Cooper problem ii 3 orbital part of the wave function spin singlet. Robert schrieffer, which is known as the bcs theory. Up to this point, there is no successful theory for the mechanism behind type ii superconductivity, though there are some experimentally. Phonon mediated attractive interaction and the cooper pairs. Bcs theory cannot explain superconductivity in these highly correlated metals. The bcs theory has been used to successfully explain the following experi mental results.
Theory of superconductivity by aalto university download. The theory describes superconductivity as a microscopic effect caused by a. 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. Bcs theory or bardeencooperschrieffer theory is the first microscopic theory of superconductivity since heike kamerlingh onness 1911 discovery. For comparison, the resistivity of copper at room temperature is. Microscopic theory bardeen, cooper, schrieffer 1957 first successful microscopic theory bcs theory. This book presents modern theory of nonstationary and nonequilibrium superconductivity. The physical mechanism of how these work is described by bcs theory. Bcs bardeencooperschrieffer theory is essentially just hartreefock theory lec.
Nuclear magnetic resonance discussed below and other experimental. We have since extended the theory to higher temperatures, have shown that it gives both a secondorder transition and a meissner effect, and have calculated specific heats and penetration depths. John schieffers book was written for solid state physicists with more than just a casual interest in superconductivity. Superconductivity is the set of physical properties observed in certain materials, wherein electrical resistance vanishes and from which magnetic flux fields are expelled. Furthermore, bcs theory has proven unable to predict any new superconducting compounds.
Bardeencooperschrieffer 1957 i the effective forces between electrons can sometimes be attractive in a solid rather than repulsive ii cooper problem. A closed path and the surface it contains within a superconductor. Electrons in a superconductor at low t are coupled in pairs coupling comes about due to interaction beween electrons and crystal lattice in a little more detail. This can happen, so the theory says, when a single negatively charged electron slightly distorts the lattice of atoms in the superconductor, drawing. A primer, microscopic theory of superconductivity, the essentials of dft and fplo, high tc superconductors. This theory is based on the idea that there is an attractive interaction between electrons caused by the phonons. Here we will discuss a new ground state of the interacting electron gas. This video lecture will explain the bcs theory of superconductivity in hindi. The book provides the microscopic theory based on the green function formalism within the bardeen, cooper, and schrieffer bcs theory. Concepts of fermi liquid theory and instability of the normal state. Lecture notes on superconductivity a work in progress. We study finite size effects in superconducting metallic grains and determine the bcs order parameter and the low energy excitation spectrum in terms of size, and shape of the grain. Bcs theory of superconductivity ii in hindi youtube. There existed no consistent microscopic theory that described why superconductivity arose, from the time it was dis.
The troubling issues range from the electrodynamics and collec. The energy gap is related to the coherence length for the superconductor, one of the two characteristic lengths associated with superconductivity. Then according to maxwells equations applicable to a superconductor equally to a normal metal the circulating current will produce its own magnetic. A theory of superconductivity formulated by john bardeen, leon cooper, and robert schrieffer. Introduction superconductivity discovered in 1911 by onnes 9, is the quantum phenomena that certain materials exhibit under particular magnetic and temperature regimes. 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.
Our approach combines the bcs selfconsistency condition, a. It explains the phenomenon in which a current of electron pairs flows without resistance in certain materials at low temperatures. The effective net attraction between the normally repulsive electrons produces a pair binding energy on the order of millielectron volts, enough to keep. Phenomenological theories of superconductivity figure 1. Bardeencooperschrieffer bcs theory of superconductivity a theory of superconductivity formulated by john bardeen, leon cooper, and robert schrieffer. We will then calculate and study interesting quantities of the superconducting system, and nally describe how the results predicted by the bcs theory fare against experimental evidence obtained about superconductors. London and london derived a phenomenological theory of su perconductivity. Bcs theory is complex, so we summarize it qualitatively below. Yet meissner and ochsenfeld found that below tc the. Still in a superconductor, even under this condition, there is a strong correlation into pairs, in which the correlation is identical for each pair, and. It deals with superconductors in external fields varying in time and studies transport phenomena in superconductors. The microscopic theory of superconductivity is an excellent example of a steady seventy years progress towards this goal which is still further going on. Superconductivity an overview sciencedirect topics. Any material exhibiting these properties is a superconductor.
Theory of superconductivity university of illinois. Robert schrieffer, for which they received the nobel prize in 1972. This theory accounts for all properties of superconductors. This superconducting state is called the bcs state and the hamiltonian they dealt with is called the bcs hamiltonian. The bcs theory explains the super conductivity of only type i superconductors and does not explain type ii superconductors. The discussion of cooper pairs, the foundation for bcs theory, though not difficult to read, is easier to understand after going through gordon bayms discussion of this topic in lectures on quantum mechanics lecture notes and supplements in physics. High temperature superconductivity, bcs theory and the mechanism of high temperature superconductivity are introduced. Bcs theory, in physics, a comprehensive theory developed in 1957 by the american physicists john bardeen, leon n. The bcs theory relies on the assumption that supercon ductivity arises when the attractive cooper pair interac tion dominates over the repulsive coulomb force. The theory is also used in nuclear physics to describe the pairing. A theory of superconductivity is presented, based on the fact that the interaction between electrons resulting from virtual exchange of phonons isattractive when. Lecture notes applied superconductivity electrical. The second order phase transition at t c ginzburg and landau, 1950. Type i superconductors, along with some type ii superconductors can be modeled using the bcs theory, proposed by john bardeen, leon cooper, and robert schrieffer.
In 1957, bardeen, cooper and schrieffer proposed 3 a quantum theory of superconductivity, known as the bcs theory, for which they received a nobel prize. The main point of the bcs theory is that the attractive electronelectron interaction mediated by the phonons gives rise to cooper pairs, i. A successful theory of superconductivity was developed in the 1950s by john bardeen, leon cooper, and j. Timeline of superconductors and their transition temperatures from wikipedia. Landau theory 9 provides a theoretical basis for the distinction between the two types. In this macroscopic quantum state, the electrons form. A hole is the absence of an electron, and hole carriers exist when an electronic energy band is almost full. In the theory, the normal state is described by the bloch individualparticle model. This paper suggests the possibility that bcs theory itself as the theory of conventional superconductivity may require a fundamental overhaul. Why does bcs theory fail to explain superconductivity at. An attractive interaction between electrons through electronlatticeelectron interaction can lead to a ground state separated from excited states by an energy gap. 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. Type ii include high temperature superconductors and can be ceramics or metals, and can have critical temperatures up to about k.
Hole superconductivity university of california, san diego. Bcs theory of superconductivity questions and answers. Cooper pairs and the bcs theory of superconductivity. Find materials for this course in the pages linked along the left.
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