Week13: Lecture 26: April 19 2021

Bose Einstein Condensate

Superconductivity

<https://www.youtube.com/watch?v=MT5Xl5ppn48>

<https://www.youtube.com/watch?v=zGPb04wg_5o>

Superconductivity is a phenomenon occurring in some materials when cooled below a

critical temperature with two key characteristics

(1) Exactly zero electrical resistance and

(2) Expulsion of magnetic fields

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It was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911 in Leiden

Applications: Two important applications are in MRI and particle accelerators. This is because

superconductors give us very powerful electromagnets.

Superconductors give us very powerful electromagnets.Two important applications are

(1) MRI

(2) particle accelerators.

(1) Superconducting magnet: An electromagnet made from coils of superconducting wire.

They must be cooled to very low temperatures during operation. In its superconducting state

the wire has no electrical resistance and therefore can conduct much larger electric currents

than ordinary wire, creating intense magnetic fields. Superconducting magnets can produce

greater magnetic fields than all but the strongest non-superconducting electromagnets and can

be cheaper to operate because no energy is dissipated as heat in the windings. The most widely

used application for superconductors is an MRI machine commonly found in hospitals. Only a

superconductive system could allow the energy required to generate a magnetic field that powers

an MRI, which can be anywhere from 2,500 times to 10,000 times the strength of Earths magnetic

field, to be economical.

(2) Another important application is in particle accelerators, like the kind used in CERN Large

Hadron Collider (LHC) or its proposed Future Circular Collider. If the MRI machine sounds

powerful, the LHC is an absolute beast. Sending trillions of particles around 27km of tunnels at

speeds close to the speed of light, keeping the particle beam stable and moving along the precise

path requires a magnetic field of immense power, more than 100,000 times the Earths magnetic

field. This requires an enormous amount of energy, the kind that superconducting coils can

provide.

The Future of Superconductivity There is a lot we do not know about superconductive

materials, and we are developing new applications for superconductors every day. The key is to

develop superconductors that are superconducting at room temperature. Possible Revolutionary

Applications

(1) The hope is to one day use superconductivity in power transmissions, which would

dramatically reduce energy costs around the world.

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(2) Mag-lev trains, which use superconductivity to hover a train car above the rail, thereby

eliminating friction that might slow a train down, may be the future of transportation.

(3) Who knows? Maybe one day we will have electronics that utilize superconductors to give us

smartphones that only need to be charged once a month or more.

With the rapid advances in our technology, we will all likely to see superconductivity in our lives

as a regular feature sooner rather than later.

UNDERSTANDING SUPERCONDUCTIVITY at microscopic level Why some materials

become superconductors ?? The complete microscopic theory of superconductivity was finally

proposed in 1957 by Bardeen, Cooper and Schrieffer, known as the BCS theory. It is purely

quantum phenomena that cannot be explained within classical theory. In short, superconductivity

is due to formation of Cooper pairs , pairs of electrons. That is, two electrons somehow pair up.

Unlike electrons, Cooper pairs are bosons. For this work, the authors were awarded the Nobel

Prize in 1972. Nobel Prizes: (1) Heike Kamerlingh Onnes (1913): Experimental Discovery of

Superconductivity: About 4 degrees Kelvin (-452 degrees Fahrenheit, -268 degrees Celsius) (2)

John Bardeen, Leon N. Cooper, and J. Robert Schrieffer (1972), “for their jointly developed

theory of superconductivity, usually called the BCS-theory” 4 (3) Georg Bednorz and Alex Miller

: 1987 - High Temperature Superconductivity: 30 degrees Kelvin

( Latest : about 134 degrees K

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