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A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. Persistent electric current flows on the surface of the superconductor, acting to exclude the magnetic field of the magnet (the Meissner effect). This current effectively forms an electromagnet that repels the magnet.
A magnet levitating above a high-temperature superconductor, cooled with liquid nitrogen. A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field. High-temperature superconductors (abbreviated high Tc or HTS) are a family of superconducting Ceramic materials largely Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of Persistent electric current flows on the surface of the superconductor, acting to exclude the magnetic field of the magnet (the Meissner effect). The Meissner effect (also known as the Jared-Ochsenfeld effect) is the expulsion of a Magnetic field from a Superconductor. This current effectively forms an electromagnet that repels the magnet.

Superconductivity is a phenomenon occurring in certain materials at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field (the Meissner effect). Materials are physical Substances used as inputs to production or Manufacturing. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges The Meissner effect (also known as the Jared-Ochsenfeld effect) is the expulsion of a Magnetic field from a Superconductor.

The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. Electrical resistivity (also known as specific electrical resistance) is a measure of how strongly a material opposes the flow of Electric current. In Science and engineering, a conductor is a material which contains movable Electric charges. However, in ordinary conductors such as copper and silver, impurities and other defects impose a lower limit. Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Even near absolute zero a real sample of copper shows a non-zero resistance. Absolute zero is the point at which molecules do not move (relative to the rest of the body more than they are required to by a quantum mechanical effect called Zero-point The resistance of a superconductor, on the other hand, drops abruptly to zero when the material is cooled below its "critical temperature". An electric current flowing in a loop of superconducting wire can persist indefinitely with no power source. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it In Physics, atomic Spectral lines are of two types An emission line is formed when an electron makes a transition from a particular discrete Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons It cannot be understood simply as the idealization of "perfect conductivity" in classical physics. A perfect conductor is an Electrical conductor with no Resistivity.

Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys and some heavily-doped semiconductors. Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 WikipediaNaming An alloy is a Solid solution or Homogeneous mixture of two or more elements, at least one of which is a Metal, which itself has In Semiconductor production doping is the process of intentionally introducing impurities into an extremely pure (also referred to as intrinsic) semiconductor to A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Superconductivity does not occur in noble metals like gold and silver, nor in most ferromagnetic metals. Noble metals are Metals that are resistant to Corrosion or Oxidation, unlike most Base metals They tend to be Precious metals often Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 Silver (ˈsɪlvɚ is a Chemical element with the symbol " Ag " (argentum from the Ancient Greek: ἀργήντος - argēntos gen Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it

In 1986 the discovery of a family of cuprate-perovskite ceramic materials known as high-temperature superconductors, with critical temperatures in excess of 90 kelvin, spurred renewed interest and research in superconductivity for several reasons. Cuprate - A compound containing copper and some other element(s especially oxygen ? ( Cuprate previously redirected to Copper oxide) From 1986 A perovskite is any material with the same type of Crystal structure as Calcium titanium oxide (CaTiO3 known as the perovskite structure The word ceramic is derived from the Greek word κεραμικός ( keramikos) High-temperature superconductors (abbreviated high Tc or HTS) are a family of superconducting Ceramic materials largely As a topic of pure research, these materials represented a new phenomenon not explained by the current theory. And, because the superconducting state persists up to more manageable temperatures, past the economically-important boiling point of liquid nitrogen (77 kelvin), more commercial applications are feasible, especially if materials with even higher critical temperatures could be discovered. The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of

Contents

Elementary properties of superconductors

Most of the physical properties of superconductors vary from material to material, such as the heat capacity and the critical temperature, critical field, and critical current density at which superconductivity is destroyed. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity

On the other hand, there is a class of properties that are independent of the underlying material. For instance, all superconductors have exactly zero resistivity to low applied currents when there is no magnetic field present. The existence of these "universal" properties implies that superconductivity is a thermodynamic phase, and thus possess certain distinguishing properties which are largely independent of microscopic details. In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties

Zero electrical "dc" resistance

Electric cables for accelerators at CERN: top, regular cables for LEP; bottom, superconducting cables for the LHC.
Electric cables for accelerators at CERN: top, regular cables for LEP; bottom, superconducting cables for the LHC. The European Organization for Nuclear Research (Organisation Européenne pour la Recherche Nucléaire known as CERN

The simplest method to measure the electrical resistance of a sample of some material is to place it in an electrical circuit in series with a current source I and measure the resulting voltage V across the sample. An electrical network is an interconnection of Electrical elements such as Resistors Inductors Capacitors Transmission lines Voltage Electrical tension (or voltage after its SI unit, the Volt) is the difference of electrical potential between two points of an electrical The resistance of the sample is given by Ohm's law as R = \frac{V}{I}. Ohm's law applies to Electrical circuits it states that the current through a conductor between two points is directly proportional to the If the voltage is zero, this means that the resistance is zero and that the sample is in the superconducting state.

Superconductors are also able to maintain a current with no applied voltage whatsoever, a property exploited in superconducting electromagnets such as those found in MRI machines. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. Experiments have demonstrated that currents in superconducting coils can persist for years without any measurable degradation. Experimental evidence points to a current lifetime of at least 100,000 years, and theoretical estimates for the lifetime of a persistent current exceed the estimated lifetime of the universe. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy

In a normal conductor, an electrical current may be visualized as a fluid of electrons moving across a heavy ionic lattice. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge The electrons are constantly colliding with the ions in the lattice, and during each collision some of the energy carried by the current is absorbed by the lattice and converted into heat, which is essentially the vibrational kinetic energy of the lattice ions. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature The kinetic energy of an object is the extra Energy which it possesses due to its motion As a result, the energy carried by the current is constantly being dissipated. This is the phenomenon of electrical resistance.

The situation is different in a superconductor. In a conventional superconductor, the electronic fluid cannot be resolved into individual electrons. Instead, it consists of bound pairs of electrons known as Cooper pairs. In Condensed matter physics, a Cooper pair is the name given to electrons that are bound together at low temperatures in a certain manner first described in 1956 by This pairing is caused by an attractive force between electrons from the exchange of phonons. In Physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the Atomic lattice of a Solid Due to quantum mechanics, the energy spectrum of this Cooper pair fluid possesses an energy gap, meaning there is a minimum amount of energy ΔE that must be supplied in order to excite the fluid. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons An energy spectrum is a distribution of Energy among a large assemblage of particles In Solid state physics and related applied fields a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states Therefore, if ΔE is larger than the thermal energy of the lattice, given by kT, where k is Boltzmann's constant and T is the temperature, the fluid will not be scattered by the lattice. Thermal energy is the sum of the sensible energy and latent energy. Bridge from macroscopic to microscopic physics Boltzmann's constant k is a bridge between Macroscopic and microscopic physics Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The Cooper pair fluid is thus a superfluid, meaning it can flow without energy dissipation. Superfluidity is a phase of matter or description of Heat capacity in which unusual effects are observed when Liquids, typically of Helium-4

In a class of superconductors known as Type II superconductors, including all known high-temperature superconductors, an extremely small amount of resistivity appears at temperatures not too far below the nominal superconducting transition when an electrical current is applied in conjunction with a strong magnetic field, which may be caused by the electrical current. A Type II superconductor is a Superconductor characterised by its gradual transition from the superconducting to the normal state within an increasing magnetic field High-temperature superconductors (abbreviated high Tc or HTS) are a family of superconducting Ceramic materials largely This is due to the motion of vortices in the electronic superfluid, which dissipates some of the energy carried by the current. If the current is sufficiently small, the vortices are stationary, and the resistivity vanishes. The resistance due to this effect is tiny compared with that of non-superconducting materials, but must be taken into account in sensitive experiments. However, as the temperature decreases far enough below the nominal superconducting transition, these vortices can become frozen into a disordered but stationary phase known as a "vortex glass". Below this vortex glass transition temperature, the resistance of the material becomes truly zero.

Superconducting phase transition

Behavior of heat capacity (cv, blue) and resistivity (ρ, green) at the superconducting phase transition
Behavior of heat capacity (cv, blue) and resistivity (ρ, green) at the superconducting phase transition

In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature Tc. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K (Kelvin) to less than 1 K. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic Solid mercury, for example, has a critical temperature of 4. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum 2 K. As of 2001, the highest critical temperature found for a conventional superconductor is 39 K for magnesium diboride (MgB2), although this material displays enough exotic properties that there is doubt about classifying it as a "conventional" superconductor. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. Magnesium diboride (MgB2 is an inexpensive and simple Superconductor. Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature of 92 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. Cuprate - A compound containing copper and some other element(s especially oxygen ? ( Cuprate previously redirected to Copper oxide) From 1986 Yttrium barium copper oxide, often abbreviated YBCO is a Chemical compound with the formula Y[[Barium Ba]]2 Cu 3 O 7 The explanation for these high critical temperatures remains unknown. Electron pairing due to phonon exchanges explains superconductivity in conventional superconductors, but it does not explain superconductivity in the newer superconductors that have a very high critical temperature. In Physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the Atomic lattice of a Solid

The onset of superconductivity is accompanied by abrupt changes in various physical properties, which is the hallmark of a phase transition. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another For example, the electronic heat capacity is proportional to the temperature in the normal (non-superconducting) regime. Specific heat capacity, also known simply as specific heat, is the measure of the heat energy required to increase the Temperature of a unit quantity At the superconducting transition, it suffers a discontinuous jump and thereafter ceases to be linear. At low temperatures, it varies instead as e−α /T for some constant α. This exponential behavior is one of the pieces of evidence for the existence of the energy gap. In Solid state physics and related applied fields a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states

The order of the superconducting phase transition was long a matter of debate. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another Experiments indicate that the transition is second-order, meaning there is no latent heat. In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase Calculations in the 1970s suggested that it may actually be weakly first-order due to the effect of long-range fluctuations in the electromagnetic field. Only recently it was shown theoretically with the help of a disorder field theory, in which the vortex lines of the superconductor play a major role, that the transition is of second order within the type II regime and of first order (i. Vorticity is a mathematical concept used in Fluid dynamics. It can be related to the amount of " circulation " or "rotation" (or more strictly the e. , latent heat) within the type I regime, and that the two regions are separated by a tricritical point. In Thermochemistry, latent heat is the amount of Energy in the form of Heat released or absorbed by a substance during a change of phase A tricritical point is a point in the Phase diagram of a system at which three-phase coexistence terminates

Meissner effect

When a superconductor is placed in a weak external magnetic field H, the field penetrates the superconductor for only a short distance λ, called the London penetration depth, after which it decays rapidly to zero. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In Superconductivity, London penetration depth (usually denoted as \lambda\ This is called the Meissner effect, and is a defining characteristic of superconductivity. The Meissner effect (also known as the Jared-Ochsenfeld effect) is the expulsion of a Magnetic field from a Superconductor. For most superconductors, the London penetration depth is on the order of 100 nm.

The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenz's law, when a changing magnetic field is applied to a conductor, it will induce an electrical current in the conductor that creates an opposing magnetic field. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect Lenz's law (ˈlɛntsɨz ˌlɔː gives the direction of the induced Electromotive force (emf and current resulting from Electromagnetic induction. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field.

The Meissner effect is distinct from this because a superconductor expels all magnetic fields, not just those that are changing. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled below the critical temperature, we would observe the abrupt expulsion of the internal magnetic field, which we would not expect based on Lenz's law.

The Meissner effect was explained by the brothers Fritz and Heinz London, who showed that the electromagnetic free energy in a superconductor is minimized provided

\nabla^2\mathbf{H} = \lambda^{-2} \mathbf{H}\,

where H is the magnetic field and λ is the London penetration depth. Fritz Wolfgang London ( March 7, 1900 &ndash March 30, 1954) was a German -born American theoretical Physicist. Heinz London ( Bonn, Germany 1907-1970 was a German Physicist In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering

This equation, which is known as the London equation, predicts that the magnetic field in a superconductor decays exponentially from whatever value it possesses at the surface. The London equations, developed by brothers Fritz and Heinz London in 1935,relate current to Electromagnetic fields in and around a A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value

The Meissner effect breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. In Type I superconductors, superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value Hc. Depending on the geometry of the sample, one may obtain an intermediate state consisting of regions of normal material carrying a magnetic field mixed with regions of superconducting material containing no field. In Type II superconductors, raising the applied field past a critical value Hc1 leads to a mixed state in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electrical current as long as the current is not too large. Magnetic flux, represented by the Greek letter Φ ( Phi) is a measure of quantity of Magnetism, taking into account the strength and the extent of a Magnetic At a second critical field strength Hc2, superconductivity is destroyed. The mixed state is actually caused by vortices in the electronic superfluid, sometimes called fluxons because the flux carried by these vortices is quantized. A fluxon is a quantum of electromagnetic flux and may have one of several meanings Electromagnetic Behavior In Theoretical physics, fluxons Most pure elemental superconductors, except niobium, technetium, vanadium and carbon nanotubes, are Type I, while almost all impure and compound superconductors are Type II. A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. Niobium (naɪˈoʊbiəm or columbium (/kəˈlʌmbiəm/ is a Chemical element that has the symbol Nb and Atomic number 41 Technetium (tɛkˈniːʃɪəm is the lightest Chemical element with no Stable isotope. Vanadium (vəˈneɪdiəm is a Chemical element that has the symbol V and Atomic number 23 See also Graphene, Buckypaper Carbon nanotubes (CNTs are Allotropes of carbon with a nanostructure that can have a length-to-diameter

Theories of superconductivity

Since the discovery of superconductivity, great efforts have been devoted to finding out how and why it works. During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957). Condensed matter physics is the field of Physics that deals with the macroscopic physical properties of Matter. Generalizations of these theories form the basis for understanding the closely related phenomenon of superfluidity, because they fall into the Lambda transition universality class, but the extent to which similar generalizations can be applied to unconventional superconductors as well is still controversial. Superfluidity is a phase of matter or description of Heat capacity in which unusual effects are observed when Liquids, typically of Helium-4 The λ (lambda Universality class is probably the most important group in Condensed matter physics. Unconventional superconductors are materials that display Superconductivity but that do not conform to BCS theory and Nikolay Bogolyubov theory or its extensions The four-dimensional extension of the Ginzburg-Landau theory, the Coleman-Weinberg model, is important in quantum field theory and cosmology. The Coleman-Weinberg model represents Quantum electrodynamics of a scalar field in four-dimensions In quantum field theory (QFT the forces between particles are mediated by other particles Cosmology (from Greek grc κοσμολογία - grc κόσμος kosmos, "universe" and grc -λογία -logia) is study

History of superconductivity

Main article: History of superconductivity

Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently-discovered liquid helium as a refrigerant. The history of superconductivity, the property exhibited by certain substances of lacking Electrical resistance at temperatures close to Absolute zero, Heike Kamerlingh Onnes ( September 21, 1853 &ndash February 21, 1926) was a Dutch Physicist. Mercury (ˈmɜrkjʊri also called quicksilver or hydrargyrum, is a Chemical element with the symbol Hg ( Latinized hydrargyrum Cryogenics is often used incorrectly to refer to Cryonics, cryopreserving humans or animals Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical A refrigerant is a compound used in a heat cycle that undergoes a Phase change from a Gas to a Liquid and back At the temperature of 4. 2 K, he observed that the resistance abruptly disappeared. [1] In subsequent decades, superconductivity was found in several other materials. In 1913, lead was found to superconduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. Characteristics Lead has a dull luster and is a dense, Ductile, very soft highly Niobium nitride is a compound of Niobium and Nitrogen with the Chemical formula NbN

The next important step in understanding superconductivity occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect. Fritz Walther Meißner (or Meissner ( December 16, 1882, Berlin &ndash November 16, 1974, Munich) was a German technical Robert Ochsenfeld was a German Physicist born on May 18 1901 in Helberhausen. The Meissner effect (also known as the Jared-Ochsenfeld effect) is the expulsion of a Magnetic field from a Superconductor. [2] In 1935, F. and H. London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current. In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering [3]

In 1950, the phenomenological Ginzburg-Landau theory of superconductivity was devised by Landau and Ginzburg. The term phenomenology in Science is used to describe a body of knowledge which relates several different empirical observations of phenomena to each other Lev Davidovich Landau ( Russian language: Ле́в Дави́дович Ланда́у ( January 22, 1908 &ndash April 1, 1968 Vitaly Lazarevich Ginzburg (Виталий Лазаревич Гинзбург born October 4 1916 in Moscow) is a Russian theoretical physicist [4]This theory, which combined Landau's theory of second-order phase transitions with a Schrödinger-like wave equation, had great success in explaining the macroscopic properties of superconductors. In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another In Physics, especially Quantum mechanics, the Schrödinger equation is an equation that describes how the Quantum state of a Physical system In particular, Abrikosov showed that Ginzburg-Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Alexei Alexeyevich Abrikosov (Алексе́й Алексе́евич Абрико́сов (born June 25, 1928) is a Russian theoretical physicist Abrikosov and Ginzburg were awarded the 2003 Nobel Prize for their work (Landau having died in 1968). The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature

Also in 1950, Maxwell and Reynolds et al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element. Isotopes (Greek isos = "equal" tópos = "site place" are any of the different types of atoms ( Nuclides A chemical element is a type of Atom that is distinguished by its Atomic number; that is by the number of Protons in its nucleus. [5] [6] This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J In Physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the Atomic lattice of a Solid

The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper, and Schrieffer. John Bardeen ( May 23 1908 – January 30 1991) was an American Physicist and Electrical engineer, who won Leon Neil Cooper (born February 28, 1930) is an American physicist and Nobel Prize laureate, who with John Bardeen and John Robert John Robert Schrieffer (born May 31, 1931) is an American physicist and with John Bardeen and Leon Neil Cooper, recipient of the [7] Independently, the superconductivity phenomenon was explained by Nikolay Bogolyubov. Nikolai Nikolaevich Bogoliubov, (Микола Миколайович Боголюбов Николай Николаевич Боголюбов ( 21 August 1909 This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. In Condensed matter physics, a Cooper pair is the name given to electrons that are bound together at low temperatures in a certain manner first described in 1956 by For this work, the authors were awarded the Nobel Prize in 1972.

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. In Quantum mechanics, the Hamiltonian H is the Observable corresponding to the Total energy of the system [8] In 1959, Lev Gor'kov showed that the BCS theory reduced to the Ginzburg-Landau theory close to the critical temperature. Lev Gor'kov (born 14 June 1928 in Moscow) is an American research physicist from Russia who is internationally known for his pioneering work in the field [9]

In 1962, the first commercial superconducting wire, a niobium-titanium alloy, was developed by researchers at Westinghouse. Founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. In the same year, Josephson made the important theoretical prediction that a supercurrent can flow between two pieces of superconductor separated by a thin layer of insulator. Brian David Josephson (born 4 January, 1940; Cardiff, Wales) is a Welsh physicist, professor and became a Nobel Prize [10] This phenomenon, now called the Josephson effect, is exploited by superconducting devices such as SQUIDs. The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier Squid are marine Cephalopods of the order Teuthida, which comprises around 300 species It is used in the most accurate available measurements of the magnetic flux quantum \Phi_0 = \frac{h}{2e}, and thus (coupled with the quantum Hall resistivity) for Planck's constant h. The magnetic flux quantum Φ0 is the Quantum of Magnetic flux passing through a Superconductor. The quantum Hall effect (or integer quantum Hall effect) is a quantum-mechanical version of the Hall effect, observed in two-dimensional electron systems The Planck constant (denoted h\ is a Physical constant used to describe the sizes of quanta. Josephson was awarded the Nobel Prize for this work in 1973.

High Temperature superconductivity

Main article: High-temperature superconductivity

Until 1986, physicists had believed that BCS theory forbade superconductivity at temperatures above about 30 K. High-temperature superconductors (abbreviated high Tc or HTS) are a family of superconducting Ceramic materials largely In that year, Bednorz and Müller discovered superconductivity in a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987). Johannes Georg Bednorz ( May 16, 1950) is a German Physicist who shared the 1987 Nobel Prize in Physics for work in High-temperature Karl Alexander Müller (born April 20, 1927) is a Swiss physicist and Nobel laureate. Lanthanum (ˈlænθənəm is a Chemical element with the symbol La and Atomic number 57 A perovskite is any material with the same type of Crystal structure as Calcium titanium oxide (CaTiO3 known as the perovskite structure [11] It was shortly found by M. K. Wu et al. that replacing the lanthanum with yttrium, i. Yttrium (ˈɪtriəm is a Chemical element with symbol Y and Atomic number 39 e. making YBCO, raised the critical temperature to 92 K, which was important because liquid nitrogen could then be used as a refrigerant (at atmospheric pressure, the boiling point of nitrogen is 77 K)[12]. Yttrium barium copper oxide, often abbreviated YBCO is a Chemical compound with the formula Y[[Barium Ba]]2 Cu 3 O 7 Liquid nitrogen (liquid density at the Triple point is 0707 g/mL is the liquid produced industrially in large quantities by Fractional distillation of This is important commercially because liquid nitrogen can be produced cheaply on-site with no raw materials, and is not prone to some of the problems (solid air plugs, et cetera) of helium in piping. Helium exists in Liquid form only at very low Temperatures The Boiling point and critical point depend on the Isotope Many other cuprate superconductors have since been discovered, and the theory of superconductivity in these materials is one of the major outstanding challenges of theoretical condensed matter physics. Condensed matter physics is the field of Physics that deals with the macroscopic physical properties of Matter.

From about 1993 the highest temperature superconductor was a ceramic material consisting of thallium, mercury, copper, barium, calcium, and oxygen, with Tc=138 K. [13]

In February, 2008, another different (no copper) family of high temperature superconductors was discovered. [14] Hideo Hosono of the Tokyo Institute of Technology and colleagues found that lanthanum oxygen fluorine iron arsenide (LaO1-xFxFeAs) becomes a superconductor at 26 kelvin. Other researchers quickly found other materials in the same family that have transition temperatures as high as 55K. Experts hope that having another family to study will simplify the task of explaining how these materials work.

Classification

Main article: Superconductor classification

There is not just one criterion to classify superconductors. Superconductors can be classified in accordance with several criteria that depend on our interest in their physical properties on the understanding we have about them on how expensive The most common are:

Applications

Main article: Technological applications of superconductivity

Superconducting magnets are some of the most powerful electromagnets known. Some of the technological applications of superconductivity include the production of Magnetometers based on SQUIDs Digital circuits A superconducting magnet is an Electromagnet that is built using superconducting coils An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. They are used in maglev trains, MRI and NMR machines and the beam-steering magnets used in particle accelerators. MAGLEV, or magnetic levitation, is a system of transportation that suspends guides and (usually propels vehicles predominantly trains using magnetic forces They can also be used for magnetic separation, where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries. For the drug referred to as "pigment" see Black tar heroin.

Superconductors have also been used to make digital circuits (e. Digital electronics are Electronics systems that use Digital signals Digital electronics are representations of Boolean algebra also see g. based on the Rapid Single Flux Quantum technology) and RF and microwave filters for mobile phone base stations. In Electronics, rapid single flux quantum ( RSFQ) is a Digital electronics technology that relies on quantum effects in Superconducting materials Radio Frequency (RF and Microwave filters represent a class of Electronic filter, designed to operate on signals in the Megahertz to Gigahertz

Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier Squid are marine Cephalopods of the order Teuthida, which comprises around 300 species A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument Series of Josephson devices are used to define the SI volt. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. Depending on the particular mode of operation, a Josephson junction can be used as photon detector or as mixer. The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument The large resistance change at the transition from the normal- to the superconducting state is used to build thermometers in cryogenic micro-calorimeter photon detectors. A calorimeter is a device used for Calorimetry, the Science of measuring the heat of Chemical reactions or Physical changes as well as Heat A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument

Other early markets are arising where the relative efficiency, size and weight advantages of devices based on HTS outweigh the additional costs involved.

Promising future applications include high-performance transformers, power storage devices, electric power transmission, electric motors (e. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors Superconducting Magnetic Energy Storage (SMES systems store energy in the Magnetic field created by the flow of Direct current in a superconducting coil Electric power transmission, a process in the delivery of Electricity to consumers is the bulk transfer of electrical power An electric motor uses Electrical energy to produce Mechanical energy. g. for vehicle propulsion, as in vactrains or maglev trains), magnetic levitation devices, and Fault Current Limiters. A vactrain is an exotic as-yet-unbuilt proposal for future high-speed Railroad transportation MAGLEV, or magnetic levitation, is a system of transportation that suspends guides and (usually propels vehicles predominantly trains using magnetic forces Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than Magnetic fields The A Fault Current Limiter (FCL is a device which limits the prospective Fault current when a fault occurs (eg in a power transmission network However superconductivity is sensitive to moving magnetic fields so applications that use alternating current (e. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant g. transformers) will be more difficult to develop than those that rely upon direct current. Direct current ( DC) is the unidirectional flow of Electric charge.

References

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  2. ^ W. Meissner and R. Ochsenfeld (1933). "Ein neuer Effekt bei Eintritt der Supraleitfähigkeit". Naturwiss. 21 (44): 787–788. doi:10.1007/BF01504252. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  3. ^ F. London and H. London (1935). "The Electromagnetic Equations of the Supraconductor". Proc. R. Soc. London A 149 (866): 71–88.  
  4. ^ V. L. Ginzburg and L. D. Landau (1950). "On the theory of superconductivity". Zh. Eksp. Teor. Fiz. 20 (1064).  
  5. ^ E. Maxwell (1950). "Isotope Effect in the Superconductivity of Mercury". Phys. Rev. 78 (4): 477. doi:10.1103/PhysRev.78.477. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  6. ^ C. A. Reynolds, B. Serin, W. H. Wright, and L. B. Nesbitt (1950). "Superconductivity of Isotopes of Mercury". Phys. Rev. 78 (4): 487. doi:10.1103/PhysRev.78.487. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  7. ^ J. Bardeen, L. N. Cooper, and J. R. Schrieffer (1957). "Theory of Superconductivity". Phys. Rev. 108 (5): 1175–1205. doi:10.1103/PhysRev.108.1175. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  8. ^ N. N. Bogoliubov (1958). "A new method in the theory of superconductivity". Zh. Eksp. Teor. Fiz. 34 (58).  
  9. ^ L. P. Gor'kov (1959). "Microscopic derivation of the Ginzburg--Landau equations in the theory of superconductivity". Zh. Eksp. Teor. Fiz. 36 (1364).  
  10. ^ B. D. Josephson (1962). "Possible new effects in superconductive tunnelling". Phys. Lett. 1 (7): 251–253. doi:10.1016/0031-9163(62)91369-0. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  11. ^ J. G. Bednorz and K. A. Mueller (1986). "Possible high TC superconductivity in the Ba-La-Cu-O system". Z. Phys. B64 (2): 189–193. doi:10.1007/BF01303701. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  12. ^ M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang, and C. W. Chu (1987). "Superconductivity at 93 K in a New Mixed-Phase Y-Ba-Cu-O Compound System at Ambient Pressure". Physical Review Letters 58: 908–910. doi:10.1103/PhysRevLett.58.908. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  13. ^ P. Dai, B. C. Chakoumakos, G. F. Sun, K. W. Wong, Y. Xin and D. F. Lu (1995). "Synthesis and neutron powder diffraction study of the superconductor HgBa2Ca2Cu3O8+δ by Tl substitution". Physica C:Superconductivity 243 (3-4): 201–206. doi:10.1016/0921-4534(94)02461-8. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
  14. ^ Adrian Cho. Second Family of High-Temperature Superconductors Discovered. ScienceNOW Daily News.

OXFORD UNIVERSITY PRESS, Oxford, United Kingdom, 2005 (ISBN 0198528159)

See also

External links

Dictionary

superconductivity

-noun

  1. (physics) The property of a material whereby it has no resistance to the flow of an electric current.
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