Abstract:
The year 2011 has witnessed the completion of 100 years of discovery of
superconductivity. It was discovered in the year 1911 by H. K. Onnes in mercury while
measuring its resistivity at low temperatures. He observed a sudden and massive drop in
resistivity below 4.2 K that was immeasurable and coined the term ‘superconducting
state’. Since the discovery of superconductivity, it has not lost its fascination and has
been an active area of research. The flow of electric current without friction amounts to
the realization of age old human dream of ‘perpetual motion’. The ratio of resistance in
normal state and the superconducting state of a metal has been tested to exceed 1014 and
thus there is every reason to assume the resistivity to be zero. Superconducting state is
therefore a ‘zero resistivity’ state. However it is not just a resistance-less phenomena but
also excludes magnetic fields from the bulk of the material. When magnetic field is
removed from a perfect conductor, the Lenz law opposes the time dependent change in
the magnetic field and the field is trapped in the material. However superconductors in
the superconducting state show complete expulsion of magnetic and therefore also are
perfect diamagnets.
