This document summarizes the key properties and mechanisms of superconductors. It begins by explaining that superconductors have zero electrical resistance below a critical temperature. It then discusses several defining features of superconductors including zero resistivity, perfect diamagnetism known as the Meissner effect, and ability to maintain currents indefinitely without power. The document outlines the BCS theory of superconductivity involving the formation of electron pairs. It also differentiates between types I and II superconductors and provides examples of each. Finally, it briefly discusses some applications of superconductors in areas like maglev trains, power transmission, and MRI machines.

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3. Superconductors is materials that
have no resistance to the flow of
electricity below a certain
temperature.

4. As the temperature drops below the critical point, Tc,
resistivity rapidly drops to zero and current can flow
freely without any resistance. Thus, superconductors
can carry large amounts of current with little or no
loss of energy.

5. 1) Zero electrical resistivity.
This means that an electrical current in a
superconducting ring continues
indefinitely until a force is applied to
oppose the current.
2) In front of external magnetic field
it act like diamagnetic material.

6. In practically
 Resistivity: s ~ 4x10-23  cm for
superconductor.
 Resistivity: m ~ 1x10-13  cm for non
superconductor metal (good conductor).

7. Does it obey the Ohm’s law???
 R = V/I
If the voltage is zero, this means that the
resistance is zero. Superconductors
are also able to maintain a current
with no applied voltage whatsoever.

8. Mechanism inside the
superconductor
 In a normal conductor, an electric current may
be visualized as a fluid of electrons moving
across a heavy ionic lattice. The electrons are
constantly colliding with the ions in the lattice,
and during each collision some of the energy
carried by the current is absorbed by the lattice
and converted into heat. As a result, the energy
carried by the current is constantly being
dissipated. This is the phenomenon of electrical
resistance.
The situation is different in a superconductor.

9. Mechanism inside the
superconductor
 In a conventional superconductor, the
electronic fluid cannot be resolved into
individual electrons. Instead, it consists
of bound pairs of electrons known as
Cooper pair. This pairing is caused by an
attractive force(ΔE) between electrons
from the exchange of phonons.
 There is a minimum amount of energy
ΔE that must be supplied in order to
excite the fluid.

10. Cont…
Therefore,
if ΔE > kT( Super fluid)
ΔE< kT(not a super fluid)
kT= thermal energy of the lattice
k = Boltzmann's constant (1.38066 x 10-23 J/K)
T = temperature of the lattice
The fluid will not be scattered by the lattice.
The Cooper pair fluid is thus a superfluid,
meaning it can flow without energy dissipation.

11. Conductor Superconductor

12. Meissner effect
When a superconductor is placed in a
weak external magnetic field H, and
cooled below its transition temperature, it
"expels" nearly all magnetic flux and from
its interior; this is called the Meissner
effect
This constraint to zero magnetic field inside
a superconductor

13. Meissner effect

14. Magnetic Levitation
 Magnetic fields are actively excluded
from superconductors (Meissner effect).
 If a small magnet is brought near a
superconductor, it will be repelled
because induced super currents will
produce mirror images of each pole.
 If a small permanent magnet is placed
above a superconductor, it can be
levitated by this repulsive force.

15. Magnetic Levitation

16. BCS Theory (1957)
John Bardeen, Leon Cooper, and John Schreiffer
The theory asserts that, as electrons pass through a
crystal lattice, the lattice deforms inward towards the
electrons generating sound packets known as
"phonons". These phonons produce a trough of
positive charge in the area of deformation that
assists subsequent electrons in passing through a
conductor will attract nearby positive charges in the
lattice. This deformation of the lattice causes another
electron, with opposite "spin", to move into the region
of higher positive charge density. The two electrons
then become correlated.

17. BCS Theory

18. phonons
According to BCS theory

19. Types I Superconductors
 There are pure metals which exhibit zero
resistivity at low temperature.
 They are called Type I superconductors
(Soft Superconductors).
 The superconductivity exists only below
their critical temperature and below a
critical magnetic field strength.

20. Mat. Tc (K)
Be 0
Rh 0
W 0.015
Ir 0.1
Lu 0.1
Hf 0.1
Ru 0.5
Os 0.7
Mo 0.92
Zr 0.546
Cd 0.56
U 0.2
Ti 0.39
Zn 0.85
Ga 1.083
Mat. Tc (K)
Gd 1.1
Al 1.2
Pa 1.4
Th 1.4
Re 1.4
Tl 2.39
In 3.408
Sn 3.722
Hg 4.153
Ta 4.47
V 5.38
La 6.00
Pb 7.193
Tc 7.77
Nb 9.46
Type I
Superconductors

21. Types II Superconductors
 Type 2 category of superconductors be
composed of metallic compounds and
alloys
 They were found to have much higher
critical fields and therefore could carry
much higher current densities while
remaining in the superconducting state.

22. Type II
Superconductors

23. High Temperature Superconductor (HTS)
 Discovered in 1986, HTS ceramics are working at 77
K, saving a great deal of cost as compared to
previously known superconductor alloys.
 However, as has been noted in a Nobel Prize
publication of Bednortz and Muller, these HTS
ceramics have two technological disadvantages:
 they are brittle and they degrade under common
environmental influences.

24. HTS Ceramics
 HTS materials the most popular is
orthorhombic YBa2Cu3O7-x (YBCO)
ceramics

25. Some high-Tc superconductors
Formula Tc (K)
YBa2Cu3O7 92
Bi2Sr2CuO6 20
Bi2Sr2CaCu2O8 85
Bi2Sr2Ca2Cu3O6 110
Tl2Ba2CuO6 80
Tl2Ba2CaCu2O8 108
Ba2Ca2Cu3O10 125
TlBa2Ca3Cu4O11 122
HgBa2CuO4 94
HgBa2CaCu2O6 128
HgBa2Ca2Cu3O8 134

26. Nobel Prize for Superconductivity
 1913 Heike Kamerlingh Onnes on Matter at low
temperature
 1972 John Bardeen, Leon N. Cooper, J. Robert
Schrieffer on Theory of superconductivity(BCS)
 1973 Leo Esaki, Ivar Giaever, Brian D. Josephson
on Tunneling in superconductors
 1987 Georg Bednorz, Alex K. Muller on High-
temperature superconductivity
 2003 Alexei A. Abrikosov, Vitaly L. Ginzburg,
Anthony J. Leggett on Pioneering contributions to
the theory of superconductors and superfluids.

27. Application
Maglev vehicles:
Magnetically levitated vehicles are called “maglev”
vehicles.
The principle of repulsion of magnetic flux can be
used in magnetic lavation application

28. The coaches of the train do not slide over
steel rails, but float on a four inch above
the track, using superconducting
magnets.
Eliminates losses due to friction.
400km/hr-500km/hr

29. APPLICATIONS: Power
 The cable configuration features a
conductor made from HTS wires
wound around a flexible hollow core.
 Ba2Ca2Cu3O10 (BCCO) discovered in
Japan. Sumitomo Electric is the world's
first company to produce long bismuth-
based superconducting wire
 Liquid nitrogen (77K) 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.

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

31. 1)http://www.superconductors.org
2)http://www.ornl.gov/info/reports/m/ornlm3063r1/pt4.html
3)http://www.chem.ox.ac.uk/vrchemistry/super/default.html
4)http://en.wikipedia.org/wiki/Superconductivity
5)M.K. Wu, J.R. Ashburn, C.J. Torng, P.H. Hor, R.L. Meng, L. Gao,
6)Z.J. Huang, Y.Q. Wang and C.W. Chu, Phys. Rev. Letters, 1987. 58, 908
7)J. File and R.G. Mills, Phys. Rev. Letters, 1963, 10, 93
8)J.G. Bednorz and K.A. Muller, Z. Phys., 1986, B64, 189
9)J.M. Tarascon, L.H. Greene, W.R. McKinnon, G.W. Hall and
10)T.H. Geballe, Science, 1987, 235, 1373
11)Chemistry in Britain, September 1994 - an issue devoted to the chemistry of 12)superconducting
materials.
13)P.A. Cox, Transition Metal Oxides, Oxford 1992
14)A.I. Nazzal, V.Y. Lee, E.M. Engler, R.D. Jacowitz, Y. Tokura and
15)J.B. Torrance, Physica C, 1988, 153 & 1367
16)Ivar Giaever - Nobel Lecture. Nobelprize.org. Retrieved 16 Dec 2010.
17)http://nobelprize.org/nobel_prizes/physics/laureates/1973/giaever-lecture.html
18)The BCS Papers:
a)L. N. Cooper, "Bound Electron Pairs in a Degenerate Fermi Gas"
b)J. Bardeen, L. N. Cooper, and J. R. Schrieffer, "Microscopic Theory of Superconductivity" (1957).
c)J. Bardeen, L. N. Cooper, and J. R. Schrieffer, "Theory of Superconductivity"(1957).
References

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