Editing Meissner effect (section)

==Consequences==
The discovery of the Meissner effect led to the [[Phenomenology (particle physics)|phenomenological]] theory of superconductivity by [[Fritz London|Fritz]] and [[Heinz London]] in 1935. This theory explained resistanceless transport and the Meissner effect, and allowed the first theoretical predictions for superconductivity to be made. However, this theory only explained experimental observations—it did not allow the microscopic origins of the superconducting properties to be identified. This was done successfully by the [[BCS theory]] in 1957, from which the penetration depth and the Meissner effect result.<ref>{{cite journal |last1=Bardeen |first1=J. |last2=Cooper |first2=L. N. |last3=Schrieffer |first3=J. R. |year=1957 |title=Theory of superconductivity |journal=[[Physical Review]] |volume=106 |issue=1175 |pages=162–164 |bibcode=1957PhRv..106..162B |doi=10.1103/physrev.106.162 |doi-access=free}}</ref> However, some physicists argue that BCS theory does not explain the Meissner effect.<ref>{{cite journal |last1=Hirsch |first1=J. E. |year=2012 |title=The origin of the Meissner effect in new and old superconductors |journal=[[Physica Scripta]] |volume=85 |issue=3 |pages=035704 |arxiv=1201.0139 |bibcode=2012PhyS...85c5704H |doi=10.1088/0031-8949/85/03/035704|s2cid=118418121 }}</ref>

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Image:Tin_4.2K_Electromagnet.jpg|A tin cylinder—in a Dewar flask filled with liquid helium—has been placed between the poles of an electromagnet. The magnetic field is about 8 [[millitesla]] (80 [[Gauss (unit)|G]]).
Image:Tin_80gauss_4.2K.jpg|''T'' = 4.2&nbsp;K, '''B''' = 8&nbsp;mT (80 G). Tin is in the normally conducting state. The compass needles indicate that magnetic flux permeates the cylinder.
Image:Tin_80gauss_1.6K.jpg|The cylinder has been cooled from 4.2&nbsp;K to 1.6&nbsp;K. The current in the electromagnet has been kept constant, but the tin became superconducting at about 3&nbsp;K. Magnetic flux has been expelled from the cylinder (the Meissner effect).
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