General Aspects of Superconductivity

Twenty years later, in 1933, the German physicist Walter Meissner (together with his co-worker Robert Ochsenfeld) discovered that superconductors cannot be crossed by magnetic field lines. This property is today defined as the Meissner effect. 

In the years that followed, attempts were made to exploit the technological potential of the two properties of superconductivity  

Unfortunately, there were two practical problems severely hindering possible applications  

To overcome these practical problems, research aimed at the preparation of new materials exhibiting superconductivity at higher and higher temperatures and able to sustain this state even in the presence of strong magnetic fields (or, also in the presence of high electric currents). 

The first objective was that of achieving critical temperatures higher than 77 K (—196°C). In this way liquid nitrogen (boiling point 77 K) could be used as the cryogenic liquid instead of the much more expensive and difficult to handle liquid helium. 

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