 Diagram of the Meissner effect. Magnetic field lines, represented as arrows, are excluded from a superconductor when it is below its critical temperature. In Physics, the Meissner effect (or Meissner-Ochsenfeld effect) is the expulsion of a magnetic field from a superconductor. The phenomenon was discovered by Walther Meissner and Robert Ochsenfeld in 1933 by measuring the flux distribution outside of tin and lead specimens as they were cooled below their transition temperature in the presence of a magnetic field. They found that below the superconducting transition temperature that the specimens became perfectly diamagnetic, cancelling all flux inside. The experiment demonstrated for the first time that superconductors were more than just perfect conductors and provided a uniquely defining property of the superconducting state. Image File history File links EfektMeisnera. ...
Image File history File links EfektMeisnera. ...
This article needs additional references or sources for verification. ...
Magnetic field lines shown by iron filings In physics, a magnetic field is a solenoidal vector field in the space surrounding moving electric charges and magnetic dipoles, such as those in electric currents and magnets. ...
Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ...
Fritz Walther Meißner (December 16, 1882, Berlin - November 16, 1974, Munich) was a German technical physicist. ...
Robert Ochsenfeld was a German physicist born on 18 May 1901 in Helberhausen. ...
1933 (MCMXXXIII) was a common year starting on Sunday. ...
Diamagnetism is a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. ...
Explanation
The Meissner effect effectively tells us that in a weak applied field, a superconductor expels all magnetic flux. Although the magnetic field is completely expelled from the interior of the superconductor, there is not a sharp transition at the edges of a sample, but rather a rapid decay of field into the sample over a distance called the penetration depth. Each superconductor will have a characteristic penetration depth dependent on the material properties. When a superconductor is cooled in a weak magnetic field and crosses below the transition temperature, persistent currents arise on the surface. They circulate so as to cancel the flux inside (c.f. a current flowing around a loop generates a perpendicular magnetic field - the superconductor does the same to generate a field which opposed the applied field. These persistent currents only flow in a depth equal to the penetration depth. Penetration Depth is a measure of how deep light or any electromagnetic radiation can penetrate into a material. ...
Perfect Diamagnetism Superconductors in the Meissner state exhibit perfect diamagnetism, or Superdiamagnetism, such that their magnetic susceptibility is -1. Diamagnetism is defined as the generation of a spontaneous magnetization of a material which directly opposes the direction of an applied field. However, the fundamental origins of the diamagnetism in superconductors and normal materials are very different. In superconductors the diamagnetism arises from the persistent screening currents which flow to oppose the applied field, in normal materials diamagnetism arises as a direct result of an orbital rotation of electrons about the nuclei of an atom induced electromagnetically by the application of an applied field. Superdiamagnetism (or perfect diamagnetism) is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of magnetic susceptibility and the exclusion of the interior magnetic field. ...
Consequences of the Meissner Effect The discovery of the Meissner effect led to the phenomenological theory of superconductivity by F. and H. London in 1935. They successfully created a theory which explained the resistance less transport and Meissner effect which allowed the first theoretical predictions for superconductivity to be made. However, their theory merely explained experimental observations it did not allow the microscopic origins of the superconducting properties to be identified. Use of the word phenomenology in modern science is described in the separate article phenomenology (science). ...
Observing the Meissner Effect Observation of the Meissner effect is a very difficult experiment, as the applied fields have to be very small (the measurements need to be made a long way from the phase boundary). This is because the penetration depth is temperature dependent and tends to infinity close to the phase boundary.
References 1. M. Tinkham, “Introduction to Superconductivity”, 2nd Ed., Dover Books on Physics (2004). ISBN 0-486-43503-2 (Paperback). A good technical reference.
2. Fritz London, "Superfluids", Volume I, "Macroscopic Theory of Superconductivity", (1950). Reprinted by Dover. ISBN 0-486-600440. By the man who explained the Meissner effect. pp.34-37 gives a technical discussion of the Meissner effect for a superconducting sphere.
3. Wayne M. Saslow, "Electricity, Magnetism, and Light", Academic (2002). ISBN 0-12-619455-6. pp.486-489 gives a simple mathematical discussion of the surface currents responsible for the Meissner effect, in the case of a long magnet levitated above a superconducting plane.
4. W. Meissner and R. Ochsenfeld, Naturwissenschaften 21, 787 (1933)
See also Wikimedia Commons has media related to: Meissner effect Image File history File links Commons-logo. ...
Superdiamagnetism (or perfect diamagnetism) is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of magnetic susceptibility and the exclusion of the interior magnetic field. ...
Helium II will creep along surfaces in order to find its own level - after a short while, the levels in the two containers will equalize. ...
Levitating pyrolytic carbon Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. ...
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