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Superconducting Materials: by Shishir

Superconducting materials are able to conduct electricity without resistance when cooled below a critical temperature. Superconductivity was discovered in 1911 and has applications in engineering, medicine, and power transmission. The BCS theory models superconductivity by electron pairing into Cooper pairs through interactions with the crystal lattice. There are two main types of superconductors - type I exhibit a sudden loss of magnetism while type II have a gradual loss and mixed state. The Meissner effect causes magnetic field expulsion in superconductors. Josephson junctions allow electron tunneling between superconductors and are used in SQUIDs for precision magnetic measurements with applications in healthcare and earthquake detection.

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86 views16 pages

Superconducting Materials: by Shishir

Superconducting materials are able to conduct electricity without resistance when cooled below a critical temperature. Superconductivity was discovered in 1911 and has applications in engineering, medicine, and power transmission. The BCS theory models superconductivity by electron pairing into Cooper pairs through interactions with the crystal lattice. There are two main types of superconductors - type I exhibit a sudden loss of magnetism while type II have a gradual loss and mixed state. The Meissner effect causes magnetic field expulsion in superconductors. Josephson junctions allow electron tunneling between superconductors and are used in SQUIDs for precision magnetic measurements with applications in healthcare and earthquake detection.

Uploaded by

shishirkmr
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© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PPTX, PDF, TXT or read online on Scribd
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Superconducting

Materials

By Shishir
Introduction
WHAT IS SUPERCONDUCTIVITY??
For some materials, the resistivity vanishes at some low temperature:
they become superconducting.

Superconductivity is the ability of


certain materials to conduct
electrical current with no resistance.
Thus, superconductors can carry
large amounts of current with little
or no loss of energy.

Superconductivity was discovered in 1911 by Heike Kammerlingh Onnes

Applications of superconductors
 Engineering field
 Medical field
BCS Theory of Superconductivity
 The properties of type I superconductors were modeled by the
efforts of John Bardeen, Leon Cooper, and Robert Schrieffer in
what is commonly called the BCS theory.
 A key conceptual element in this theory is the pairing of electrons
close to the Fermi level into Cooper pairs through interaction
with the crystal lattice.
 This pairing results from a slight attraction between the electrons
related to lattice vibrations; the coupling to the lattice is called a
phonon interaction.
Types of Superconductors
Type I Type II
 Sudden loss of  Gradual loss of
magnetisation magnetisation
 Exhibit Meissner Effect  Does not exhibit complete
 One HC = 0.1 tesla Meissner Effect
 No mixed state  Two HCs – HC1 & HC2 (≈30
 Soft superconductor tesla)
 Eg.s – Pb, Sn, Hg  Mixed state present
 Hard superconductor
 Eg.s – Nb-Sn, Nb-Ti
Occurrence of Superconductivity

Superconducting Elements TC (K)


Sn (Tin) 3.72
Hg (Mercury) 4.15
Pb (Lead) 7.19
Superconducting Compounds
NbTi (Niobium Titanium) 10
Nb3Sn (Niobium Tin) 18.1
MEISSNER EFFECT

When the superconducting material is placed in a magnetic field under the


condition when T≤TC and H ≤ HC, the flux lines are excluded from the material.

Material exhibits perfect diamagnetism or flux exclusion.

B B

T>Tc T<Tc

Levitation of a magnet by superconductor


Applications of Meissner Effect
Standard test – proof for a superconductor
Repulsion of external magnets - levitation

Magnet

Superconductor

Yamanashi MLX01 MagLev train

430 km/h = 267.2 mph


APPLICATIONS:
Superconducting
Magnetic Levitation

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. In addition, a wave of electric current
sweeps down these outside coils and propels the train
forward.

The Yamanashi MLX01MagLev Train


JOSEPHSON EFFECT

A Josephson junction is made up of two superconductors, separated by a


nonsuperconducting layer so thin that electrons can cross through the insulating barrier.
The flow of current between the superconductors in the absence of an applied voltage is
called a Josephson current,
 the movement of electrons across the barrier is known as Josephson tunneling.
 Two or more junctions joined by superconducting paths form what is called a Josephson
interferometer.
SQUIDS
Types
Two main types of SQUID:
1) RF SQUIDs have only one Josephson junction
2)DC SQUIDs have two or more junctions.
Thereby,
 more difficult and expensive to produce.
 much more sensitive.

uses
Study of earthquakes
Removing paramagnetic impurities
Detection of magnetic signals from brain, heart etc.
OF
APPLICATION
SUPER
CONDUCTORS
Applications
Large distance power transmission (ρ = 0)

Switching device (easy destruction of


superconductivity)
Sensitive electrical equipment (small V variation 
large constant current)
Memory / Storage element (persistent current)
Highly efficient small sized electrical generator and
transformer
Medical Applications
•NMR – Nuclear Magnetic Resonance –
Scanning
•Brain wave activity – brain tumour, defective
cells
•Separate damaged cells and healthy cells
Power Transmission in USA
 2001: Detroit, USA
› Detroit Edison at the Frisbie Substation
› three 400-foot HTS cables
› 100 million watts of power

http://www.ornl.gov/sci/fed/applied/htspa/cable.htm
THANK
YOU

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