Skip to main content

BCS THEORY ON SUPERCONDUCTIVITY

BCS theory on superconductors.

This theory was proposed by three scientists Bardeen, Cooper and Schrieffer in 1957. 
This theory explains about zero resistance of a superconductor.
In normal substances the flow of free electrons is opposed by the vibration of ions or atoms in the lattice due to the collision between them. Hence the normal conductors possess resistance.
In the case of superconductors below the critical temperature (Tc), the atom or the ion is distorted by the free electron during the collision. 
The result produces a mechanical wave called phonon.
During this collision the free electron exchanges an amount of its momentum with the lattice ion.
Hence the momentum of free electron in reduced. It moves with less momentum.
If another free electron collides with the distorted lattice ion (phonon), the second electron gains an amount of momentum from the phonon. Hence the second free electron moves with greater
momentum.
But the change in momentum for the two free electrons is equal and they move with opposite momentum and spin. This pair of electrons is called Cooper pair.
The motion of Cooper pair of electrons is not effected by adding impurities and any change in Thermal characteristics. Hence there will be no deviation in the flow of Cooper pair. This is the reason for zero resistance of superconductors.


--------------------------------------------------------------------------------

Comments

Popular posts from this blog

UNIT CELL AND LATTICE PARAMETERS

Unit cell In Crystals the arrangement of particles is described with three dimensional geometrical  parallelepiped structure.  The unit cell is defined as the smallest size of parallelepiped structure with  minimum number of atoms. In a unit cell there are 6 faces and 8 corners. So 8 atoms are required to form a unit cell and all the  8 atoms are located at the 8 corners each. Lattice Lattice is defined as a three dimensional array of atoms. It describes the size and shape of the unit cell. Parameters of a unit cell A unit cell is described by six parameters. These parameters are three dimensions  and the  angles between them . The Dimensions of unit cell  along three axes of a unit cell are represented by (a, b ,c) . The angle between b and c is represented by α, between a and c by β and between a and b by γ. we can identify the structure of crystal by knowing the parameters of unit cell. Properties of unit cell : 1. Unit cell is...

BRAVIAS CRYSTALS -7 CRYSTAL SYSTEMS

Bravias crystals : There are 7 different basic crystal lattices according to the dimensions (a,b,c) and their angles( ⍺ , 𝛽, ℽ )  of unit cell which are called Bravias crystals.  1 Cubic crystal system :                   a=b=c  and α=β=γ=90  example : NaCl available systems are simple cubic, face centered and body centered cubic systems 2 Tetragonal                a=b ≠ c and  α=β=γ=90  example SiSO4 available systems : simple and body centered cubic systems. 3 Orthorhombic                        a ≠ b ≠c and  α=β=γ=90 example: BaSO4 available systems are simple, body centered ,face centered and base centered cubic systems. . 4 Monoclinic (rhombohedral )                    a ≠ b ≠c and  α=β=90γ=120 example:  Na2So4...

MEISNER EFFECT ON SUPERCONDUCTORS

Meissner effect.