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Superdiamagnetism
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<h2 id="theory">Theory</h2> <p><a href="/facts/Fritz_London/9NvJ4MR7">Fritz London</a> and <a href="/facts/Heinz_London/TMhHQxbe">Heinz London</a> developed the theory that the exclusion of <a href="/facts/Magnetic_flux/jQMVxrnD">magnetic flux</a> is brought about by <a href="/facts/Electrical/hNC8D65W">electrical</a> screening currents that flow at the surface of the superconducting material and which generate a <a href="/facts/Magnetic_field/Ta8Ev588">magnetic field</a> that exactly cancels the externally applied field inside the superconductor. These screening currents are generated whenever a superconducting material is brought inside a magnetic field. This can be understood by the fact that a superconductor has zero electrical resistance, so that <a href="/facts/Eddy_current/KvHNx1v7">eddy currents</a>, induced by the <a href="/facts/Motion_(physics)/dCnP7MlB">motion</a> of the material inside a magnetic field, will not decay. Fritz, at the <a href="/facts/Royal_Society/KI5yXCuV">Royal Society</a> in 1935, stated that the <a href="/facts/Thermodynamic/q4hIx3yP">thermodynamic</a> state would be described by a single <a href="/facts/Wave_function/KgM5ykjY">wave function</a>. </p><p>"Screening currents" also appear in a situation wherein an initially normal, conducting metal is placed inside a magnetic field. As soon as the metal is cooled below the appropriate transition temperature, it becomes superconducting. This expulsion of magnetic field upon the cooling of the metal cannot be explained any longer by merely assuming <a href="/facts/Zero/4NBRtKHc">zero</a> resistance and is called the <i><a href="/facts/Meissner_effect/VJLdDzzE">Meissner effect</a></i>. It shows that the superconducting state does not depend on the history of preparation, only upon the present values of <a href="/facts/Temperature/QyGe4gmj">temperature</a>, <a href="/facts/Pressure/eyc37GRG">pressure</a> and magnetic field, and therefore is a true <a href="/facts/Thermodynamic_state/Rv6m11Pf">thermodynamic state</a>. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Superfluidity/QuePDujN">Superfluidity</a></li> <li><a href="/facts/Timeline_of_low-temperature_technology/UhxEyE4Y">Timeline of low-temperature technology</a></li></ul> <ul><li>Shachtman, Tom, <i>Absolute Zero: And the Conquest of Cold</i>. Houghton Mifflin Company, December 1999. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 0-395-93888-0</li></ul>