A Presentation on “Superconductivity “

Guided By:- Youman sir

Prepared By:-Laxmikant vermaM.Sc physics (final)3rd sem

SESSION 2014-15

(ALL PHYSICS DEPARTMENT)

Synopsis

INTRODUCTIONWHAT IS SUPERCONDUCTORDIFFERENCE BETWEEN PERFECT CONDUCTOR

AND SUPERCONDUCTORPROPERTY ON SUPERCONDUCTOR FURTHER RESEARCH SUGGESTIONS ON

SUPERCONDUCTORCONCLUSION

History of SuperconductivityHelium liquefier completed in 1908 in

Leiden

Superconductivity first observed in 1911 by Kamerlingh Onnes

Meissner effect discovered in 1933

First superconducting magnet made in 1954 by George Ynetma

Yttrium Barium Copper Oxide superconductor with a transition temperature of 90 K developed in 1987

Figure b: Walther Meissner

Figure a: Kamerlingh Onnes (left) and Van der Waals (right)

Introduction

Difference between Perfect Conductor & Superconductor

In perfect conductor resistance has low but superconductor material has resistance present exactly zero.

Mostly conductor no need to want temperature but superconductor occur only on critical temperature (Tc).

What is Superconductivity?

Superconductivity is a state of thermodynamical equilibrium that affects a material's electric and magnetic properties.

Superconductivity arises from an attractive interaction between pairs of conducting electrons, and their interaction with lattice vibrations

It can be achieved by lowering the material temperature below its critical temperature

Antiferromagnetism and Theory In 1957, Bardeen, Cooper, and Schrieffer (BCS) theorized

that superconductivity was the result of electrons binding to form particles called Cooper pairs

The electrons exchange vibrational lattice energy called phonons which can result in the electrons becoming attracted to one another

Recently, antiferromagnetism has been linked to the explanation of high temperature ceramic superconductivity

By changing the chemical composition, BaFe2(As1-xPx)2 has been observed to have an internal magnetic critical point

As the composition is changed, antiferromagnetism decreases until it disappears, resulting in superconductivity

Basic Principles

Electricity:Properties of Superconductors

Below a critical temperature (Tc), the resistance of a superconducting material becomes almost zero causing current to flow indefinitely and with no power loss

No voltage difference is needed to maintain a current.

Above a current density, superconductivity is lost in the material.

A supercurrent can flow across an insulating junction in what is called the Josephson Effect. Cooper pairs can do this due to quantum tunneling

Properties of Superconductors

ELECTRICITYMAGNETISM

Magnetism:Properties of Superconductors

Superconductors can be classified into two types according to their interaction with an external magnetic field:

Type I

Type I superconductors expel all magnetic flux

Superconductivity ends when a critical flux is applied. Examples include mercury, lead, and tin.

Magnetism:Properties of Superconductors

Type II

Type II superconductors, unlike type I, have two critical fields.

After the first critical field is reached, magnetic flux partially penetrates the material and it enters a state of mixed normal and superconductivity.

After the second critical flux is passed, superconductivity abruptly ends. Type II superconductors usually have higher critical temperatures.

Examples include YBCO, vanadium, and BSCCO

Magnetism:Properties of Superconductors

The phenomena of expelling magnetic flux experienced by superconductors is called the Meissner Effect.

The Meissner Effect can be understood as perfect diamagnetism, where the magnetic moment of the material cancels the external field or M = - H.

Superconductor Conductor

MetalsSome metals become superconductors

at extremely low temperatures

Some of these include mercury, lead, tin, aluminum, lead, niobium, cadmium, gallium, zinc, and zirconium

Unfortunately, the critical temperatures are too low for practical application

For example, Aluminum has a Tc of only 1.20K, nearly impossible to reach by conventional methods

Further Research Suggestions:Electrical

If a high critical temperature superconductor is developed that has a critical temperature that is higher than HBCCO (133 K), more practical applications will become feasible

Electrical power transmission through superconducting materials and wire o Low power losso Low voltage required for high currento Utilizes less physical space

Computer signal transmission o Low resistivity allows for computing

speed to increase greatly

High Tc Ceramics

Yttrium Barium Copper Oxide was the first superconductor developed with a Tc above the boiling point of Nitrogen (Tc=90 K).

Thallium Barium Calcium Copper Oxide has the highest Tc out of all superconductors (Tc=125 K)

This suggests that the electrons interact strongly with the positions of copper and oxygen in the lattice (Cooper pair).

Antiferromagnetism must be eliminated for superconductivity to appear.

CopperIron

Further Research Suggestions:Electrical

Figure :- Example of a superconducting cable. The liquid nitrogen coolant is part of the cable in order to keep the superconductor wire below the critical temperature. These cables can greatly reduce the physical space needed in our electrical infrastructure.

Further Research Suggestions:Magnetic

Some applications are used today:o Magnetic Resonance Imagingo Nuclear Magnetic Resonance Spectroscopy

Future applications can benefit from interesting magnetic properties displayed by superconductors

Particle Accelerators

Magnetic Levitation o High-Speed Magnetic Levitation Trains for mass

transport o By utilizing levitation, friction between the train and

the track is eliminatedo This can allow trains to increase their speed

dramatically

Metal Alloys

Metal alloys like Nb-Ti, and Nb-Zr are usually Type II superconductors

Metal Alloys have higher critical temperatures and magnetic fluxes than pure metals.

As a consequence of their properties, they are more useful for practical applications than pure metals

Conclusion

Superconductivity is a state of thermodynamical equilibrium where the electrical resistance is 0 and that is achieved at near 0 K temperatures

Superconducting ceramic materials have shown the most promise for future technologies because of their relatively high critical temperatures Figure :- Structural

interpretation of a ceramic superconductor.