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Andreev reflection, 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.
Diagram of Andreev reflection. An electron meeting the interface between a normal conductor and a superconductor produces a Cooper pair in the superconductor and a retroreflected electron hole in the normal conductor. Legend: "N" = normal conductor, "S" = superconductor, red = electron, green = hole. Arrows indicate the spin band occupied by ...
These materials are type-II superconductors with substantial upper critical field H c2, and in contrast to, for example, the cuprate superconductors with even higher H c2, they can be easily machined into wires. Recently, however, 2nd generation superconducting tapes are allowing replacement of cheaper niobium-based wires with much more ...
Conversely, the (gapless) electron order present in the normal metal is also carried over to the superconductor in that the superconducting gap is lowered near the interface. The microscopic model describing this behavior in terms of single electron processes is called Andreev reflection. It describes how electrons in one material take on the ...
Phase diagram (B, T) of a type I superconductor : if B < B c, the medium is superconducting. T c is the critical temperature of a superconductor when there is no magnetic field. The interior of a bulk superconductor cannot be penetrated by a weak magnetic field, a phenomenon known as the Meissner effect. When the applied magnetic field becomes ...
The size of the critical current (which can be as large as 100 amperes in a 1-mm wire) depends on the nature and geometry of the specimen and is related to whether the magnetic field produced by the current exceeds the critical field at the surface of the superconductor.
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. [1] The superconductor must be a type-II superconductor because type-I superconductors cannot be penetrated by magnetic fields. [2]
If a BCS superconductor with a ground state consisting of Cooper pair singlets (and center-of-mass momentum q = 0) is subjected to an applied magnetic field, then the spin structure is not affected until the Zeeman energy is strong enough to flip one spin of the singlet and break the Cooper pair, thus destroying superconductivity (paramagnetic or Pauli pair breaking).