Phenomenon of superconductivity was first observed by Kamerlingh Onnes in Leiden in 1911 ,3 years after he first liquefied helium gas. He observed that electrical resistivity of such as mercury, tin, lead completely disappear i.e., suddenly dropped to zero in a small range of temperature at a critical temperature TC which is the characteristics of the material. This happens when the specimen is cooled down to sufficiently low temperature about few degrees of Kelvin. At critical temperature TC specimen undergoes a phase transition from normal electrical resistivity state to superconducting state. Magnetic properties exhibited by superconductors are as interesting as its electrical properties. Now imagine what happened when a specimen known to exhibit superconductivity is placed in a magnetic field and then cooled through the transition temperature for superconductivity. In this case magnetic field originally present in the specimen is ejected out from the specimen and this is nothing but the Meissner Effect.
What is SuperConductors
- Superconductivity is the physical properties which is seen in certain materials, wherein electrical resistance vanishes and from which magnetic flux fields are expelled. These certian material exhibiting these properties are called superconductor.
- We see in an ordinary metallic conductor resistance decreases gradually as its temperature is lowered even down to near absolute zero but in a superconductor resistance drops abruptly to zero below characteristic critical temperature . An electric current through a loop of superconducting wire can persist indefinitely with no power source
Examples of Superconductors
Chemical elements: mercury ,lead
alloys: niobium–titanium, germanium–niobium, and niobium nitride
ceramics : YBCO and magnesium diboride
organic superconductors :fullerenes and carbon nanotubes
Information i had given here in this page is nothing but a mere definition of superconductivity phenomenon. It is a very vast topic and has a lot in it.