MOI UNIVERSITY Eldoret, Kenya  Founded in 1984

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	MOI UNIVERSITY 3rd INAUGURAL LECTURE BY PROF. K. M. KHANNA
Date :	27th March 2008
Venue :	Kerio Hall, Chepkoilel Campus
Topic :	SUPERCONDUCTIVITY
Speaker :	Prof. K. M. Khanna, Ph.D, Department of Physics, School of Science

Synopsis

The vanishing of the electrical resistance of a conductor at very low temperatures is known as the phenomena of superconductivity. It was discovered by H-K Onnes in 1911 at Leiden, Holland. He found that when the temperature of pure frozen mercury was reduced below 4.2, its electrical resistance disappeared resulting in the flow of large electrical currents. A great number of pure metals; alloys and doped semiconductors were found to have this property.

It is also found that the metals cooled in the superconducting state in a moderate magnetic field expels the magnetic field from its interior resulting in negative susceptibility of the material and this is the property of a diamagnetic material. Thus a superconducting material is a diamagnetic and this is called Meissner effect that was discovered in 1933 by Meissner et al.

The superconductivity exhibited by metals, alloys and doped semiconductors is nowadays called conventional superconductivity. The first successful theory to explain the properties of superconductors was given in 1957 by Bardeen, Cooper and Schrieffer, now known as the BCS Theory.

The transition temperature for the conventional superconductors is 23.21K or less and this is obtained using liquid helium which is a very costly liquid. This put a limit on the large scale practical applications of various superconducting materials.

But in 1986 came the break through when superconductivity was discovered in some oxides and insulators whose transition temperatures were in the range 30K to 90K. Such systems are called high-temperature superconductors. These days liquid nitrogen, which is much cheaper, is used to obtain high-temperature superconducting state.

It is found that the BCS Theory is not able to explain the phenomena of high-temperature superconductivity. A number of theories have been proposed to explain the properties of the high-temperature superconductors but none can be considered as a successful theory. Hence high-temperature superconductivity is still awaiting a successful theory.

For More Information, Contact:
Prof. K. M. Khanna (PhD)
Department of Physics,
School of Science,
Moi University

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