In 1911, the team led by Dutch physicist Heike Kamerlingh observed that the electrical resistance of mercury(Hg) goes to zero when the temperature drops below 4.2K. This was the first observation for the phenomenon of superconductivity .
The temperature at which zero resistance is observed is called as the Transition temperature(Tc) and the materials exhibiting them are called as superconductors.
For superconductors, post zero resistance, electrical current is circulated in the material without any dissipation. Also, if a weak external magnetic field is applied, it will not penetrate the superconductor but will remain at the surface. This field expulsion is known as Meissner effect and it was observed in 1933.
The microscopic theory for superconductivity was established by Bardeen, Cooper, and Schrieffer(BCS) in 1957. This theory though was unable to explain High-Temperature Superconductivity.
Researchers at the George Washington University have been able to create a minuscule sample of a hydrogen-rich compound of Lanthanum at very high pressure which exhibited superconductivity even at higher temperatures (up to 280 K)
- M. Somayazulu et. al.,’Evidence for Superconductivity above 260 K in Lanthanum Superhydride at Megabar Pressures.’ Physical Review Letters, 2019; 122 (2)
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- Bardeen et al.,‘Theory of superconductivity’, Physical Review 108 (5), 1175, 1957