Electrical Resistance Below Their Critical Temperatures example essay topic

web. The BCS theory (after is proponents US physicists John Bardeen, Leon Cooper and John Schrieffer) explains superconductivity in terms of electron pairs and packets of sound waves related to lattice vibrations (called phonons)... At temperatures below the critical temperature for particular metals (or metal alloys), the movement of electrons is enhanced by lattice vibrations (phonons) which cause electric field effects resulting in electron pairing (by overcoming what would normally be strong repulsive forces between like charges) and an assisted passage through the lattice with negligible energy loss... At temperatures below the critical temperature for the particular conductor, the cooper pairs (as the electron pairs are called) stay together. Because resistance is effectively zero, very narrow wires can carry very large currents.

The lower the temperature, below the critical temperature, the higher that current can be. That current produces a magnetic field around the conductor. The strength of the magnetic field will reach a point where it will cause the loss of the superconducting state thus putting an effective limit on the current that can flow in any particular superconductor... The practical application of superconductors is based on the combination of critical temperature (Tc the point below which superconductivity occurs), the critical field (Hc the strength above which superconductivity is stopped) and the current density (Jc above which superconductivity ceases).

BCS Theory suggests that superconductors have zero electrical resistance below their critical temperatures because at such temperatures the electrons pass unimpeded through the crystal lattice and therefore lose no energy. The theory states that the super current in a superconductor is carried by many millions of bound electron pairs, called Cooper pairs. web. BCS Theory: Bardeen, Cooper and Schrieffer Theory. BSC proposed that electron in superconductors combine in pairs in the conductivity process. These "cooper pairs" were able to by pass the obstacles in the lattice structure which are responsible for electric resistance. It was known that electrons which are the same charge would normally repel each other.

It was proposed that at very low temperatures there must be an overwhelming attractive force between the electrons to form a cooper pair... BCS theory proposed that as negatively charged electron passed positive ions in the crystal lattice, the lattice structure was distorted toward the electron. It is this positive trough that attracts the second electron forming a cooper pair which travel together through the lattice together unimpeded. The positive ions of the lattice spring back into their position once the cooper pair has passed through.