Superconductivity is a property of some materials (certain metals, alloys, organic compounds, and ceramics) in which the material loses all resistance to the flow of electricity. Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, a Dutch physicist. he was measuring the resistance of frozen mercury when he discovered an incredible drop off as the temperature neared absolute zero.

Two things hindered development in the field of superconductivity.. Firstly, the phenomenon only occurred near absolute zero, requiring liquid helium as a coolant, which is not easy to use, and secondly, no one understood why the phenomenon happened at all. It is still not entirely understood, but the modern theory is the one John Bardeen, Leon N. Cooper, and John Robert Schreffer received the 1972 Nobel Prize for Physics in, called the BCS theory. The theory states that superconductivity happens because of an attractive interaction between electrons that results in the electrons pairing up and dancing a superconductive jig.

Recently, superconductivity has been revived by the 1986 discovery of high(er) temperature superconducting ceramics by J. Georg Bednorz and K. Alex Muller. These ceramics superconduct at temperatures that can be reached using liquid nitrogen, which is much easier to use than liquid helium. The study of superconductivity continues to evolve as new applications for superconductivity are achieved, and new ones are thought of.

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There are two types of superconductivity: type 1 and type 2. Type 1 is generally seen in pure elements, while type 2 is usually seen in specially prepared superconducing alloys.

Type 1 superconductivity is much less resistant to magnetic fields and "high" temperatures. In a type 1 material, it is either fully superconducting or not superconducting at all (i.e. there is only one transistion point)

Type 2 superconductivity acts like type 1 until a certain transition point. Once past that first transition point, some atoms of the material is superconducting while others are not. The material still acts like a superconductor in this state. It is not until the second transition point that the material loses all its superconductivity. The second transition point is usually much higher than the transition point of type 1, so type 2 materials keep their superconductivity under much higher magnetic field intensities and temperatures.

Type 1 materials usually can only be superconducting at liquid helium temperatures and under very low magnetic fields of a small fraction of a tesla. However, some type 2 materials can keep up their superconducting properties at liquid nitrogen temperatures and under large fields of several teslas!

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