Superconducting properties of nanostructured cuprates, nitrides and bulk iron chalcogenides

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.