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For some materials resistivity vanishes at low temperature.


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Definition For some materials, the resistivity vanishes at some low temperature; they become Superconductive. Superconductors have the ability to conduct electrical current with no resistance (!!!), thus no loss of energy.

Discovery of Superconductivity:

Discovery of Superconductivity Superconductivity was first discovered in 1911 by the Dutch physicist,Heike Kammerlingh Onnes . Onnes, felt that a cold wire's resistance would dissipate. This suggested that there would be a steady decrease in electrical resistance, allowing for better conduction of electricity. At some very low temperature point, scientists felt that there would be a leveling off as the resistance reached some ill-defined minimum value allowing the current to flow with little or no resistance. Onnes passed a current through a very pure mercury wire and measured its resistance as he steadily lowered the temperature. Much to his surprise there was no resistance at 4.2K.

The Discovery:

The Discovery At 4.2K, the Electrical Resistance (opposition of a material to the flow of electrical current through it) Vanished, Meaning Extremely Good Conduction of Electricity-Superconductivity

Science of Superconductivity:

Science of Superconductivity The behavior of electrons inside a superconductor is vastly different. The impurities and lattice framework are still there, but the movement of the superconducting electrons through the obstacle course is quite different. As the superconducting electrons travel through the conductor they pass unobstructed through the complex lattice. Because they bump into nothing and create no friction they can transmit electricity with no appreciable loss in the current and no loss of energy.

The Science:

The Science Regular materials’ Superconductors’ 3 dimensional structure layered structure

The Science…:

The Science… A metal can be imagined as a lattice of positive ions. Electrons moving through the lattice constitute an electric current. Normally, the electrons repel each other and are scattered by the lattice, creating resistance. In superconductors, the flow of electrons is also different. It was first explained by BCS theory. The BCS theory realized that atomic lattice vibrations forced the electrons to pair up into teams ( COOPER PAIRS ) that could pass all of the obstacles which caused resistance in the conductor.

Cooper Pair ::

Cooper Pair : Two electrons that appear to "team up" in accordance with theory - BCS or other - despite the fact that they both have a negative charge and normally repel each other. Below the superconducting transition temperature, paired electrons form a condensate - a macroscopically occupied single quantum state - which flows without resistance. This pairing is caused by an attractive force between electrons from the exchange of phonons.

Animation of Cooper pairs:

Animation of Cooper pairs

The Science….:

The Science…. The superconducting state is defined by three very important factors: critical temperature (T), critical field ( H) , and critical current density (J). Each of these parameters is very dependant on the other two properties present critical temperature (T) The highest temperature at which superconductivity occurs in a material. Below this transition temperature T the resistivity of the material is equal to zero. critical magnetic field (H) Above this value of an externally applied magnetic field a superconductor becomes nonsuperconducting. critical current density (J) The maximum value of electrical current per unit of cross-sectional area that a superconductor can carry without resistance.

Meissner Effect:

Meissner Effect T > T c Superconductors have negative susceptibility. If a superconductor is cooled below its critical temperature while in a magnetic field, the magnetic field surrounds but does not penetrate the superconductor. The magnet induces current in the superconductor which creates a counter-magnetic force that causes the two materials to repel. T < T c

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Levitation of a magnet above a cooled superconductor

Types of Superconductors::

Types of Superconductors: The Meissner state breaks down when the applied magnetic field is too large. Superconductors can be divided into two classes according to how this breakdown occurs. Type I Superconductors: superconductivity is abruptly destroyed when the strength of the applied field rises above a critical value H. Most pure elemental superconductors, except niobium, technetium, vanadium and carbon nanotubes, are Type I . Type II Superconductors: In Type II superconductors, raising the applied field past a critical value Hc1 leads to a mixed state (also known as the vortex state) in which an increasing amount of magnetic flux penetrates the material, but there remains no resistance to the flow of electric current as long as the current is not too large. At a second critical field strength Hc2, superconductivity is destroyed. almost all impure and compound superconductors are Type II.

Critical Temperature of some Superconductors:

Critical Temperature of some Superconductors Material Critical Temp. (K) Y 0.01 Al 1.20 Hg 4.15 Pb 7.20 Nb3Sn 18.00 LaBaCuO 40.00 YBCuO 92.00 BiSr2Ca2Cu3Ox 113.00 HgBaCaCuO 134.00

Josephson Effect:

Josephson Effect The Josephson effect is the phenomenon of supercurrent to flow across the insulators(!!). If an insulator is sandwitched between one superconductor & one normal conductor (or two superconductors), at some voltage,current flows due to tunneling of cooper pair.


Applications Today superconductivity is being applied to many diverse areas such as: medicine, theoretical and experimental science, the military, transportation, power production, electronics as well as many other areas.

Magnetically Levitated Trains (MagLev):

Magnetically Levitated Trains (MagLev) Japanese levitating train has superconducting magnets onboard. The track are walls with a continuous series of vertical coils of wire mounted inside. The wire in these coils is not a superconductor. As the train passes each coil, the motion of the superconducting magnet on the train induces a current in these coils, making them electromagnets.The electromagnets on the train and outside produce forces that levitate the train and keep it centered above the track.

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MagLev uses Electromagnetic Propulsion. Trains are thrust forward by positively and negatively charged magnets. The train floats on a cushion of air eliminating friction.

Application in Medical:

Application in Medical MRI (Magnetic Resonance Imaging) scans produce detailed images of soft tissues. The superconducting magnet coils produce a large and uniform magnetic field inside the patient's body.

Application in Power:

Application in Power The cable configuration features a conductor made from HTS wires wound around a flexible hollow core. Liquid nitrogen flows through the core, cooling the HTS wire to the zero resistance state. The conductor is surrounded by conventional dielectric insulation. The efficiency of this design reduces losses.

Economic Impact of Superconducting Equipment:

Economic Impact of Superconducting Equipment Utilities Higher density transmission uses & higher economic productivity Reduced environmental impact Industrial More cost effective industrial processes: Manufacturing & energy production Electrical storage, transmission and expansion Transportation More cost effective electrical transportation: High Speed Rail & MAGLEV technologies Electric car / bus Ship

Worldwide Market for Superconductivity:

Worldwide Market for Superconductivity

The dream - “Tomorrow’s Superconducting World” :

The dream - “Tomorrow’s Superconducting World” *Energy saving: Power cable, motor, generator *Computing: 1000 times faster supercomputers *Information Technology: much faster, wider band communication *350mph levitated trains *Magnetically launched space shuttle & moreover.


Refferences Inspired from an essay “EK ADHORA SWAPNO” in bengali magazine “DESH” written by Mr. Pathik Guha, writer & journalist of ABP group. “Integrated Electronics”- Jacob Millman, Christos C. Halkias “Superconductivity Elementary”- Keshav N Shrivastava “Superconductivity Fundamentals & Applications”- Prof. Dr. Werner Buckel, Prof. Dr. Reinhold Kleiner WEBSITES: wikipedia

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