Super conuctivity and its future applications

This ppt gives detail about superconductivity and its application

1. Department of physics Name –David Kumar M s.c.(3 rd semester) Topic of presentation:- SUPERCONDUCTIVITY

2. SUPERCONDUCTIVITY Introduction :- Meissner effect:- Types of superconductors:- BCS Theory:- Properties of superconductivity:- Applications and future aspects:- Problems faces :- Conclusions : -

3. DEFINITION OF SUPERCONDUCTIVITY :- Superconductivity is the ability of certain materials to conduct direct current (DC) electricity with almost no resistance when cooled below a critical temperature (Tc). DISCOVERY :- It was observed first by kamerlingh Onnes in Leiden in 1911,three years after he first liquefied He At 4.2K. Critical temperature:- The temperature at which electrical resistance becomes zero is called “ critical temperature “

4. Meissner effect:- Meissner and Ochsenfeld discovered in 1933 that a superconductor expelled the magnetic flux as the former was cooled below critical temperature in an external magnetic field. i.e. It behaved as a perfect diamagnet.This phenomenon is known as Meissner effect.

5. Type 1 and Type ll superconductors:- This type of s.c. Not follow Meissner effect strictly . Type 1(soft) superconductors :- It is strictly follow the Meissner effect These s.c. Exhibit perfect diamagnetism. The field penetrate the material beyond Hc (critical field) and it come in Normal state. E.g. –Al,Zn,Hg. There Hc is always to low that is reason it is not useful for application point of view. Type II(Hard superconductors:-

6. There are characterized by two critical field Hc 1 and Hc 2 . The transition from superconducting state to normal state occurs gradually as H is increased from Hc 1 to Hc 2 . Below the Hc 1 it has pure s.c. State. Between the Hc 1 to Hc 2 it is in mixed state. At the Hc 2 it penetrate the s.c. Wall and become normal conductor. B.C.S. Theory:- Bardeen–Cooper–Schrieffer (BCS) theory is a microscopic theory of superconductivity that was developed in 1957 by American physicists John Bardeen, Leon N. Cooper, and John R. Schrieffer. To explain the behaviour of super electrons in superconductors for this work they were awarded Nobel prize In 1972.

7. BCS Theory is based on two major concepts:- Electron phonon electron Interaction Cooper pair Electron phonon electron interaction:- when an electron moves through the lattice, it will be attracted by the core(+Ve)ions of the lattice. Due to the attracting ion core is disturbed and it is called the lattice distortion. The lattice vibrations are quantised in terms of phonons. The deformation product a region of increased positive charge,. Thus If another electron moves through this region .It will be attracted by the greater concentration of positive charge and hence the Energy of the 2 nd electron is lowered. Hence the two electrons interact through the lattice the pronounce field resulting in lowering of energy of the electron this loading of energy implies that the force between the two electrons are attractive this type of interaction is called electron phone on electron interaction the interaction is strong only when the two electron have equal and opposite momentum and spins

8. Cooper pair:- Cooper pair is the name given to electron that are bound together in a certain manner first described by Leon Cooper in normal superconductors attraction is due to the electron interaction The Cooper pair state forms the basis of the BCS theory of superconductivity. Properties of Cooper pair :- When a metal is cooled to the critical temperature electron in the metal form copper pairs. Cooper pairs are electrons which exchange phone ones and become bound together. Bound electrons behaves like bosons their wave functions don’t obey pauli exclusion rule and they can all occupy the same Quantum state

9. Properties of the superconductivity:- Isotope effect:- It has been observed that critical temperature varies with isotopic mass. i .e. , critical temperature is inversely proportional to the square root of mass of the isotope. 2.Behavior of Magnetic field intensity:- Removal of the superconductivity state does not only occur by raising the temperature, but also buy subject in a material to a magnetic field. Tc=k/√m Here k is constant

10. Specific Heat effect:- A finite jump in the specific heat is observed at the critical temperature. In a superconducting face the electron resistance change with the jump while the energy undergoes a continuous variation When the substance is cooled its specific heat typically decreases but at the critical temperature it increases suddenly At low temperatures electronic specific heat contribution dominates lattice contribution .

11. Entropy effect:- In case of the superconducting material atoms has more arranged because below the critical temperature entropy decreases significantly. For Al, the change in entropy was observed to be small of the order of 10-¹⁴ k per atom, where k is Boltzmann constant . At below Tc- At above Tc- S N >S S S N <S S

12. JOSEPHSON EFFECT:- The Josephson effect is a quantum phenomenon in physics . It describes the flow of a dissipation less current between two superconductors . That are close together but separated by a barrier or restriction.
The Josephson effect describes the transfer of Cooper pairs and the coupling of macroscopic wave functions between the two superconductors through a weak link .

13. DC Josephson effect:- The DC Josephson effect describes the magnitude of the superconducting pair current when there is no applied voltage. The current is determined by the difference in the quantum mechanical phases of the superconducting states on either side of the tunnel barrier. AC Josephson effect :- The AC Josephson effect is a phenomenon that occurs when a fixed voltage is applied across a junction time. This results in a sinusoidal alternating current (AC) with a specific amplitude and frequency. fig .Dc Josephson curve

14. Applications:- Superconducting Super Collider (SSC ):- The SSC is a racetrack-shaped collider that is expected to extend particle physics research to higher level of energy—about 20 T ev . Superconducting Generators :- Superconducting generators enjoy three potential benefits over conventional generators. They offer better system stability against frequency changes due to transients on the grid 3. Magnetic Resonance Imaging (MRI) :- superconductivity was introduced early into the life cycle of MRI, with the first imager built in 1978 and the first superconducting system introduced only 2 years 1ater. 4. Defence and sensors:- used in submarine detection, Infra-red detection.

15. Future aspects:- High temperature superconductors :- HTS defined as materials with critical temperature (the temperature below which the material behaves as a superconductor) above 77 K eg . Liquid nitrogen. It is very useful for our future generations because we can easily achieve SUPERCONDUCTIVITY at high temperature. The majority of high-temperature superconductors are ceramic materials, rather than the previously known metallic materials. It is a bismuth strontium calcium copper oxide .which is the most practical high temperature superconducting material.

16. Conclusions :- That the superconductivity is the most important discovery in the field of modern physics. The advantage of the superconductors their capability of carrying enormous Amount of power without loss under critical temperature. So superconductors to save lot of energy . Research is currently underway to obtain high temperature superconductors References .:- C .kittle Institute of superconductivity .