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Abrikosov Vortices
In superconductivity, fluxon (also called a Abrikosov vortex and quantum vortex) is a vortex of supercurrent in a type-II superconductor, used by Alexei Abrikosov to explain magnetic behavior of type-II superconductors. Abrikosov vortices occur generically in the Ginzburg–Landau theory of superconductivity. Overview The solution is a combination of fluxon solution by Fritz London, combined with a concept of core of quantum vortex by Lars Onsager. In the quantum vortex, supercurrent circulates around the normal (i.e. non-superconducting) core of the vortex. The core has a size \sim\xi — the superconducting coherence length (parameter of a Ginzburg–Landau theory). The supercurrents decay on the distance about \lambda (London penetration depth) from the core. Note that in type-II superconductors \lambda>\xi/\sqrt. The circulating supercurrents induce magnetic fields with the total flux equal to a single flux quantum \Phi_0. Therefore, an Abrikosov vortex is often calle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
YBCO Vortices
Yttrium barium copper oxide (YBCO) is a family of crystalline chemical compounds that display high-temperature superconductivity; it includes the first material ever discovered to become superconducting above the boiling point of liquid nitrogen (77 K) at about 93 K. Many YBCO compounds have the general formula Y Ba2 Cu3 O7−''x'' (also known as Y123), although materials with other Y:Ba:Cu ratios exist, such as Y Ba2 Cu4 Oy (Y124) or Y2 Ba4 Cu7 Oy (Y247). At present, there is no singularly recognised theory for high-temperature superconductivity. It is part of the more general group of rare-earth barium copper oxides (ReBCO) in which, instead of yttrium, other rare earths are present. History In April 1986, Georg Bednorz and Karl Müller, working at IBM in Zurich, discovered that certain semiconducting oxides became superconducting at relatively high temperature, in particular, a lanthanum barium copper oxide becomes superconducting at 35 K. This oxide was an oxyge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetic Flux Quantum
The magnetic flux, represented by the symbol , threading some contour or loop is defined as the magnetic field multiplied by the loop area , i.e. . Both and can be arbitrary, meaning can be as well. However, if one deals with the superconducting loop or a hole in a bulk superconductor, the magnetic flux threading such a hole/loop is actually quantized. The (superconducting) magnetic flux quantum ≈ is a combination of fundamental physical constants: the Planck constant and the electron charge . Its value is, therefore, the same for any superconductor. The phenomenon of flux quantization was discovered experimentally by B. S. Deaver and W. M. Fairbank and, independently, by R. Doll and M. Näbauer, in 1961. The quantization of magnetic flux is closely related to the Little–Parks effect, but was predicted earlier by Fritz London in 1948 using a phenomenological model. The inverse of the flux quantum, , is called the Josephson constant, and is denoted J. It is the constan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nielsen–Olesen Vortex
In theoretical physics, a Nielsen–Olesen vortex is a point-like object localized in two spatial dimensions or, equivalently, a classical solution of field theory with the same property. This particular solution occurs if the configuration space of scalar fields contains non-contractible circles. A circle surrounding the vortex at infinity may be "wrapped" once on the other circle in the configuration space. A configuration with this non-trivial topological property is called the Nielsen–Olesen vortex, after Holger Bech Nielsen and Poul Olesen (1973). The solution is formally identical to the solution of Quantum vortex in superconductor. See also * Nielsen–Olsen string * Abrikosov vortex *Montonen–Olive duality *S-duality In theoretical physics, S-duality (short for strong–weak duality, or Sen duality) is an equivalence of two physical theories, which may be either quantum field theories or string theories. S-duality is useful for doing calculations in theoret ... R ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Josephson Effect
In physics, the Josephson effect is a phenomenon that occurs when two superconductors are placed in proximity, with some barrier or restriction between them. It is an example of a macroscopic quantum phenomenon, where the effects of quantum mechanics are observable at ordinary, rather than atomic, scale. The Josephson effect has many practical applications because it exhibits a precise relationship between different physics quantities, such as voltage and frequency, facilitating highly accurate measurements. The Josephson effect produces a current, known as a supercurrent, that flows continuously without any voltage applied, across a device known as a Josephson junction (JJ). These consist of two or more superconductors coupled by a weak link. The weak link can be a thin insulating barrier (known as a superconductor–insulator–superconductor junction, or S-I-S), a short section of non-superconducting metal (S-N-S), or a physical constriction that weakens the superconductivit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Andreev Reflection
Andreev reflection (AR), named after the Russian physicist Alexander F. Andreev, is a type of particle scattering which occurs at interfaces between a superconductor (S) and a normal state material (N). It is a charge-transfer process by which normal current in N is converted to supercurrent in S. Each Andreev reflection transfers a charge ''2e'' across the interface, avoiding the forbidden single-particle transmission within the superconducting energy gap. Overview The process involves an electron (hole) incident on the interface from the normal state material at energies less than the superconducting energy gap. The incident electron (hole) forms a Cooper pair in the superconductor with the retroreflection of a hole (electron) of opposite spin and velocity but equal momentum to the incident electron (hole), as seen in the figure. The barrier transparency is assumed to be high, with no oxide or tunnel layer which reduces instances of normal electron-electron or hole-hole s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pinning Force
Pinning force is a force acting on a pinned object from a pinning center. In solid state physics, this most often refers to the vortex pinning, the pinning of the magnetic vortices ( magnetic flux quanta, Abrikosov vortices) by different kinds of the defects in a type II superconductor. Important quantities are the ''individual'' maximal pinning force, which defines the depinning of a single vortex, and an ''average'' pinning force, which defines the depinning of the correlated vortex structures and can be associated with the critical current density (the maximal density of non-dissipative current). The interaction of the correlated vortex lattice with system of pinning centers forms the magnetic phase diagram of the vortex matter in superconductors. This phase diagram is especially rich for high temperature superconductors ( HTSC) where the thermo-activation processes are essential. The pinning mechanism is based on the fact that the amount of grain boundary area is reduced ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Macroscopic Quantum Phenomena
Macroscopic quantum phenomena are processes showing quantum behavior at the macroscopic scale, rather than at the atomic scale where quantum effects are prevalent. The best-known examples of macroscopic quantum phenomena are superfluidity and superconductivity; other examples include the quantum Hall effect and topological order. Since 2000 there has been extensive experimental work on quantum gases, particularly Bose–Einstein condensates. Between 1996 and 2016 six Nobel Prizes were given for work related to macroscopic quantum phenomena. Macroscopic quantum phenomena can be observed in superfluid helium and in superconductors, but also in dilute quantum gases, dressed photons such as polaritons and in laser light. Although these media are very different, they are all similar in that they show macroscopic quantum behavior, and in this respect they all can be referred to as quantum fluids. Quantum phenomena are generally classified as macroscopic when the quantum states are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flux Pinning
Flux pinning is a phenomenon that occurs when flux vortices in a type-II superconductor are prevented from moving within the bulk of the superconductor, so that the magnetic field lines are "pinned" to those locations. The superconductor must be a type-II superconductor because type-I superconductors cannot be penetrated by magnetic fields. Some type-I superconductors can experience the effects of flux pinning if they are thin enough. If the material's thickness is comparable to the London penetration depth, the magnetic field can pass through the material. The act of magnetic penetration is what makes flux pinning possible. At higher magnetic fields (above Hc1 and below Hc2) the superconductor allows magnetic flux to enter in quantized packets surrounded by a superconducting current vortex (see Quantum vortex). These sites of penetration are known as flux tubes. The number of flux tubes per unit area is proportional to the magnetic field with a constant of proportionality equal t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Upper Critical Field
For a given temperature, the critical field refers to the maximum magnetic field strength below which a material remains superconducting. Superconductivity is characterized both by perfect conductivity (zero resistance) and by the complete expulsion of magnetic fields (the Meissner effect). Changes in either temperature or magnetic flux density can cause the phase transition between normal and superconducting states.High Temperature Superconductivity, Jeffrey W. Lynn Editor, Springer-Verlag (1990) The highest temperature under which the superconducting state is seen is known as the critical temperature. At that temperature even the weakest external magnetic field will destroy the superconducting state, so the strength of the critical field is zero. As temperature decreases, the critical field increases generally to a maximum at absolute zero. For a type-I superconductor the discontinuity in heat capacity seen at the superconducting transition is generally related to the slope of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Upper Critical Field
For a given temperature, the critical field refers to the maximum magnetic field strength below which a material remains superconducting. Superconductivity is characterized both by perfect conductivity (zero resistance) and by the complete expulsion of magnetic fields (the Meissner effect). Changes in either temperature or magnetic flux density can cause the phase transition between normal and superconducting states.High Temperature Superconductivity, Jeffrey W. Lynn Editor, Springer-Verlag (1990) The highest temperature under which the superconducting state is seen is known as the critical temperature. At that temperature even the weakest external magnetic field will destroy the superconducting state, so the strength of the critical field is zero. As temperature decreases, the critical field increases generally to a maximum at absolute zero. For a type-I superconductor the discontinuity in heat capacity seen at the superconducting transition is generally related to the slope of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bessel Function
Bessel functions, first defined by the mathematician Daniel Bernoulli and then generalized by Friedrich Bessel, are canonical solutions of Bessel's differential equation x^2 \frac + x \frac + \left(x^2 - \alpha^2 \right)y = 0 for an arbitrary complex number \alpha, the ''order'' of the Bessel function. Although \alpha and -\alpha produce the same differential equation, it is conventional to define different Bessel functions for these two values in such a way that the Bessel functions are mostly smooth functions of \alpha. The most important cases are when \alpha is an integer or half-integer. Bessel functions for integer \alpha are also known as cylinder functions or the cylindrical harmonics because they appear in the solution to Laplace's equation in cylindrical coordinates. Spherical Bessel functions with half-integer \alpha are obtained when the Helmholtz equation is solved in spherical coordinates. Applications of Bessel functions The Bessel function is a generali ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type-II Superconductors
In superconductivity, a type-II superconductor is a superconductor that exhibits an intermediate phase of mixed ordinary and superconducting properties at intermediate temperature and fields above the superconducting phases. It also features the formation of magnetic field vortices with an applied external magnetic field. This occurs above a certain critical field strength ''Hc1''. The vortex density increases with increasing field strength. At a higher critical field ''Hc2'', superconductivity is destroyed. Type-II superconductors do not exhibit a complete Meissner effect. History In 1935, Rjabinin and Shubnikov experimentally discovered the Type-II superconductors. In 1950, the theory of the two types of superconductors was further developed by Lev Landau and Vitaly Ginzburg in their paper on Ginzburg–Landau theory. In their argument, a type-I superconductor had positive free energy of the superconductor-normal metal boundary. Ginzburg and Landau pointed out the possibi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
