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Josephson Vortex
In superconductivity, a Josephson vortex (after Brian Josephson from Cambridge University) is a quantum vortex of supercurrents in a Josephson junction (see Josephson effect). The supercurrents circulate around the vortex center which is situated inside the Josephson barrier, unlike Abrikosov vortices in type-II superconductors, which are located in the superconducting condensate. Abrikosov vortices (after Alexei Abrikosov) in superconductors are characterized by normal cores where the superconducting condensate is destroyed on a scale of the superconducting coherence length ''ξ'' (typically 5-100 nm) . The cores of Josephson vortices are more complex and depend on the physical nature of the barrier. In Superconductor-Normal Metal-Superconductor (SNS) Josephson junctions there exist measurable superconducting correlations induced in the N-barrier by proximity effect from the two neighbouring superconducting electrodes. Similarly to Abrikosov vortices in superconductors, Jos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superconductivity
Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source. The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes. Like ferromagnetism and atomic spectral lines, superconductivity is a phenomenon which can only be explained by quantum mechanics. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor during its transitions into the sup ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superconductor-Insulator-Superconductor
The superconducting tunnel junction (STJ) — also known as a superconductor–insulator–superconductor tunnel junction (SIS) — is an electronic device consisting of two superconductors separated by a very thin layer of insulating material. Current passes through the junction via the process of quantum tunneling. The STJ is a type of Josephson junction, though not all the properties of the STJ are described by the Josephson effect. These devices have a wide range of applications, including high-sensitivity detectors of electromagnetic radiation, magnetometers, high speed digital circuit elements, and quantum computing circuits. Quantum tunneling All currents flowing through the STJ pass through the insulating layer via the process of quantum tunneling. There are two components to the tunneling current. The first is from the tunneling of Cooper pairs. This supercurrent is described by the ac and dc Josephson relations, first predicted by Brian David Josephson in 1962. For ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shape Waves
Shape waves are excitations propagating along Josephson vortices or fluxons. In the case of two-dimensional Josephson junctions (thick long Josephson junctions with an extra dimension) described by the 2D sine-Gordon equation, shape waves are distortions of a Josephson vortex line of an arbitrary profile. Shape waves have remarkable properties exhibiting Lorentz contraction and time dilation similar to that in special relativity. Position of the shape wave excitation on a Josephson vortex In superconductivity, a Josephson vortex (after Brian Josephson from Cambridge University) is a quantum vortex of supercurrents in a Josephson junction (see Josephson effect). The supercurrents circulate around the vortex center which is situated ... acts like a “minute-hand” showing the time in the rest-frame associated with the vortex. At some conditions, a moving vortex with the shape excitation can have less energy than the same vortex without it. References * Waves {{phys ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Josephson Penetration Depth
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] |
Fluxon
In physics, a fluxon is a quantum of electromagnetic flux. The term may have any of several related meanings. Superconductivity In the context of superconductivity, in type II superconductors fluxons (also known as Abrikosov vortices) can form when the applied field lies between B_ and B_. The fluxon is a small whisker of normal phase surrounded by superconducting phase, and Supercurrents circulate around the normal core. The magnetic field through such a whisker and its neighborhood, which has size of the order of London penetration depth \lambda_L (~100 nm), is quantized because of the phase properties of the magnetic vector potential in quantum electrodynamics, see magnetic flux quantum for details. In the context of long Superconductor-Insulator-Superconductor Josephson tunnel junctions, a fluxon (aka Josephson vortex) is made of circulating supercurrents and has ''no'' normal core in the tunneling barrier. Supercurrents circulate just around the mathematical center of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semifluxon
In superconductivity, a semifluxon is a half integer vortex of supercurrent carrying the magnetic flux equal to the half of the magnetic flux quantum . Semifluxons exist in the 0-π long Josephson junctions at the boundary between 0 and π regions. This 0-π boundary creates a π discontinuity of the Josephson phase. The junction reacts to this discontinuity by creating a semifluxon. Vortex's supercurrent circulates around 0-π boundary. In addition to semifluxon, there exist also an antisemifluxon. It carries the flux and its supercurrent circulates in the opposite direction. Mathematically, a semifluxon can be constructed by joining two tails of conventional (integer) fluxon (kink of the sine-Gordon equation) at the 0-π boundary. Semifluxon is a particular example of the ''fractional vortex pinned at the phase discontinuity'', see Fractional vortices for details. For the first time the semifluxons were observed at the tricrystal grain boundaries in d-wave superconductors and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Long Josephson Junction
In superconductivity, a long Josephson junction (LJJ) is a Josephson junction which has one or more dimensions longer than the Josephson penetration depth \lambda_J. This definition is not strict. In terms of underlying model a ''short Josephson junction'' is characterized by the Josephson phase \phi(t), which is only a function of time, but not of coordinates i.e. the Josephson junction is assumed to be point-like in space. In contrast, in a long Josephson junction the Josephson phase can be a function of one or two spatial coordinates, i.e., \phi(x,t) or \phi(x,y,t). Simple model: the sine-Gordon equation The simplest and the most frequently used model which describes the dynamics of the Josephson phase \phi in LJJ is the so-called perturbed sine-Gordon equation. For the case of 1D LJJ it looks like: where subscripts x and t denote partial derivatives with respect to x and t, \lambda_J is the Josephson penetration depth, \omega_p is the Josephson plasma frequency, \omega_c is t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fractional Vortices
In a standard superconductor, described by a complex field fermionic condensate wave function (denoted , \Psi, e^), vortices carry quantized magnetic fields because the condensate wave function , \Psi, e^ is invariant to increments of the phase \phi by 2\pi. There a winding of the phase by 2\pi creates a vortex which carries one flux quantum. See quantum vortex. The term Fractional vortex is used for two kinds of very different quantum vortices which occur when: (i) A physical system allows phase windings different from 2\pi \times \mathit, i.e. non-integer or fractional phase winding. Quantum mechanics prohibits it in a uniform ordinary superconductor, but it becomes possible in an inhomogeneous system, for example, if a vortex is placed on a boundary between two superconductors which are connected only by an extremely weak link (also called a Josephson junction); such a situation also occurs in some cases in polycrystalline samples on grain boundaries etc. At such superconduc ... [...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] |
Proximity Effect (superconductivity)
Proximity effect or Holm–Meissner effect is a term used in the field of superconductivity to describe phenomena that occur when a superconductor (S) is placed in contact with a "normal" (N) non-superconductor. Typically the critical temperature T_ of the superconductor is suppressed and signs of weak superconductivity are observed in the normal material over mesoscopic distances. The proximity effect is known since the pioneering work by R. Holm and W. Meissner. They have observed zero resistance in SNS pressed contacts, in which two superconducting metals are separated by a thin film of a non-superconducting (i.e. normal) metal. The discovery of the supercurrent in SNS contacts is sometimes mistakenly attributed to Brian Josephson's 1962 work, yet the effect was known long before his publication and was understood as the proximity effect. Origin of the effect Electrons in the superconducting state of a superconductor are ordered in a very different way than in a normal meta ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brian David Josephson
Brian David Josephson (born 4 January 1940) is a Welsh theoretical physicist and professor emeritus of physics at the University of Cambridge. Best known for his pioneering work on superconductivity and quantum tunnelling, he was awarded the Nobel Prize in Physics in 1973 for his prediction of the Josephson effect, made in 1962 when he was a 22-year-old PhD student at Cambridge University. Josephson is the only Welshman to have won a Nobel Prize in Physics. He shared the prize with physicists Leo Esaki and Ivar Giaever, who jointly received half the award for their own work on quantum tunnelling."Brian D. Josephson" ''Encyclopædia Britannica''. Josephson has spent his academic career as a member of the Theory of Condensed Matter group at Cambridge's [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coherence Length
In physics, coherence length is the propagation distance over which a coherent wave (e.g. an electromagnetic wave) maintains a specified degree of coherence. Wave interference is strong when the paths taken by all of the interfering waves differ by less than the coherence length. A wave with a longer coherence length is closer to a perfect sinusoidal wave. Coherence length is important in holography and telecommunications engineering. This article focuses on the coherence of classical electromagnetic fields. In quantum mechanics, there is a mathematically analogous concept of the quantum coherence length of a wave function. Formulas In radio-band systems, the coherence length is approximated by :L = \frac \approx \frac ~, where \, c \, is the speed of light in a vacuum, \, n \, is the refractive index of the medium, and \, \mathrm f \, is the bandwidth of the source or \, \lambda \, is the signal wavelength and \, \Delta \lambda \, is the width of the range of wavelengths i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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