National Conference on Recent Trends in Engineering & Technology
Review on Superconductivity:
The Phenomenon occurred at Low Temperature
M. J. Patel, M. E. (Cryogenics),
D. H. Agrawal, M. E. (Cryogenics),
A. M. Pathan, M. E. (Cryogenics),
Mechanical Engineering Department,
L. D. College of Engineering,
Ahmedabad (INDIA),
[email protected]
Abstract—Superconductivity is a phenomenon at nano-scopic level
that does not exist in nature (although very recently the first known
superconducting mineral, ‘covellite’, was surprisingly discovered).
A superconductor shows no electrical resistance to the flow of an
electrical current (up to a value named critical current) if cooled
below a given temperature (its critical temperature) and in presence
of a magnetic field not exceeding a certain critical value. Since
1911, a huge number of superconductors have been synthesized,
with constantly increasing critical temperature, whose record value
currently exceeds 150 K (-120 °C). This paper gives an overview on
history of superconductivity and fundamental properties of
superconductors.
It also focuses on classification of
superconductors, certain superconducting materials and high
temperature superconductivity. Finally, it shows certain basic
technological applications of superconductivity.
Mechanical Engineering Department,
L. D. College of Engineering,
Ahmedabad (INDIA),
interest in the topic because of the prospects for improvement
and potential room-temperature superconductivity. From a
practical perspective, even 90 K is relatively easy to reach
with readily available liquid nitrogen (which has a boiling
point of 77 K), resulting in more experiments and applications
[1].
Keywords—Superconductivity, Cryogenics, HTS, LTS, Tc, Hc,
Cuprates
I.
INTRODUCTION
Superconductivity is an electrical resistance of exactly zero
which occurs in certain materials below a characteristic
temperature. It was discovered by Heike Kamerlingh Onnes in
1911 [3]. Like ferromagnetism and atomic spectral lines,
superconductivity is a quantum mechanical phenomenon. It is
also characterized by a phenomenon called the Meissner
effect, the ejection of any sufficiently weak magnetic field
from the interior of the superconductor as it transitions into the
superconducting state. The occurrence of the Meissner effect
indicates that superconductivity cannot be understood simply
as the idealization of perfect conductivity in classical physics.
The electrical Resistivity of a metallic conductor decreases
gradually as the temperature is lowered. However, in ordinary
conductors such as copper and silver, this decrease is limited
by impurities and other defects. Even near absolute zero, a real
sample of copper shows some resistance. Despite these
imperfections, in a superconductor the resistance drops
abruptly to zero when the material is cooled below its critical
temperature. An electric current flowing in a loop of
superconducting wire can persist indefinitely with no power
source [2]. In 1986, it was discovered that some cuprate
ceramic materials have critical temperatures above 90 K
(−183 °C). These high-temperature superconductors renewed
13-14 May 2011
Figure 1. Dependence of resistance on temperature, found for a
Superconductor.
II.
HISTORY OF SUPERCONDUCTIVITY
Superconductivity was discovered in 1911 by Heike
Kamerlingh Onnes, who was studying the resistance of solid
mercury at cryogenic temperatures using the recently
discovered liquid helium as a refrigerant. At the temperature
of 4.2 K, he observed that the resistance abruptly disappeared
[3]. He initially thought that his apparatus had shorted out.
Only later did he realize that the effect was real. In subsequent
decades, superconductivity was found in several other
materials. In 1913, lead was found to superconduct at 7 K, and
in 1941 niobium nitride was found to superconduct at 16 K.
The next important step in understanding superconductivity
occurred in 1933, when Meissner and Ochsenfeld discovered
that superconductors expelled applied magnetic fields, a
phenomenon which has come to be known as the Meissner
effect. In 1935, F. and H. London showed that the Meissner
effect was a consequence of the minimization of the
electromagnetic free energy carried by superconducting
current [4].
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
In 1950, the phenomenological Ginzburg-Landau theory of
superconductivity was devised by Landau and Ginzburg [5].
This theory, which combined Landau's theory of second-order
phase transitions with a Schrödinger-like wave equation, had
great success in explaining the macroscopic properties of
superconductors. In particular, Abrikosov showed that
Ginzburg-Landau theory predicts the division of
superconductors into the two categories now referred to as
Type I and Type II. Abrikosov and Ginzburg were awarded
the 2003 Nobel Prize for their work (Landau had received the
1962 Nobel Prize for other work, and died in 1968) [5].
Also in 1950, Maxwell and Reynolds et al. found that the
critical temperature of a superconductor depends on the
isotopic mass of the constituent element [6][7]. This important
discovery pointed to the electron-phonon interaction as the
microscopic mechanism responsible for superconductivity.
The complete microscopic theory of superconductivity was
finally proposed in 1957 by Bardeen, Cooper and Schrieffer.
Independently, the superconductivity phenomenon was
explained by Nikolay Bogolyubov. This BCS theory explained
the superconducting current as a superfluid of Cooper pairs,
pairs of electrons interacting through the exchange of
phonons. For this work, the authors were awarded the Nobel
Prize in 1972. The BCS theory was set on a firmer footing in
1958, when Bogoliubov showed that the BCS wave unction,
which had originally been derived from a variational
argument, could be obtained using a canonical transformation
of the electronic Hamiltonian. In 1959, Lev Gor'kov showed
that the BCS theory reduced to the Ginzburg-Landau theory
close to the critical temperature.
In 1962, the first commercial superconducting wire, a
niobium-titanium alloy, was developed by researchers at
Westinghouse, allowing the construction of the first practical
superconducting magnets. In the same year, Josephson made
the important theoretical prediction that a supercurrent can
flow between two pieces of superconductor separated by a thin
layer of insulator. This phenomenon, now called the
Josephson Effect, is exploited by superconducting devices
such as SQUIDs. It is used in the most accurate available
measurements of the magnetic flux quantum Фo = h/2e, and
thus (coupled with the quantum Hall Resistivity) for Planck's
constant h. Josephson was awarded the Nobel Prize for this
work in 1973. In 2008, it was discovered that the same
mechanism that produces superconductivity could produce a
super insulator state in some materials, with almost infinite
electrical resistance.
III.
vibration such as the impurity and lattice defects in real
materials. The situation is quite different in superconductors.
The material which looses the resistance at particular
temperature above 0 K (at 0 K the material loosing its
resistance is known as perfect/ideal conductor) is termed as
superconductor and the temperature at which this phenomenon
of disappearance of resistance occurs is known as transition
temperature or Critical Temperature Tc. This state of zero
resistance in material above 0 K is believed to be due the
formation of cooper pairs in the material. Bardeen, Cooper and
Schrieffee showed in 1957 that at 0 K, an electron with a
momentum moving the lattice can collide with the intermediate
temperature 0<T<Tc, the material contains copper pairs as well
as the normal electrons.
B. Meissner Effect
Another property of a superconductor is that once the
transition from the normal state to the superconducting state
occurs, external magnetic fields can not penetrate it. This
effect is called the Meissner Effect and has implications for
making high speed, magnetically-levitated trains. It also has
implications for making powerful, small, superconducting
magnets for Nuclear Magnetic Resonance (NMR).
Figure 2. Meissner Effect.
C. Josephson Effect [2]
One final property of superconductors is that when two of
them are joined by a thin, insulating layer, it is easier for the
electron pairs to pass from one superconductor to another
without resistance is called as Josephson Effect. This effect
has implications for super fast electrical switches that can be
used to make small, high-speed computers.
FUNDAMENTAL PROPERTIES OF
SUPERCONDUCTOR
A. Zero Resistance
In ideal cases, the Resistivity (ρ) of any pure metal should
decrease to zero smoothly as the temperature approaches the
absolute zero. In Practice however, ρ can never become zero,
first due to unattainably of absolute zero and secondly, because
of presence of other scattering centers, besides the lattice
13-14 May 2011
Figure 3. Josephson Effect.
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
IV.
CLASSIFICATION OF SUPERCONDUCTOR
A. By their physical properties:
Type I Superconductor:
There is a single value of the critical field at which the
transition from superconducting to normal behavior is abrupt
called soft superconductor.
Examples: Mercury, Lead, Tin
Type II Superconductor:
There is a lower Critical field HC1 at which transition begins
and an upper critical field HC2 at which transition is
completed.
Examples: Niobium, vanadium
Critical Field (Hc):
The magnetic field required to destroy the superconductivity is
called critical field (HC). The unit of critical field is Tesla.
B. Based on Critical Temperature (Tc):
D. Based on Materials:
Pure elements:
Lead and mercury. But not all pure elements are
superconductors, as some never reach the superconducting
phase. Most superconductors made of pure elements are type I
except niobium, technetium, vanadium, silicon.
Allotropes of carbon:
Fullerenes, nano-tubes, diamond etc...
Alloys:
Niobium-Titanium (NbTi) (discovered in1962), NbN, Nb3Ge
etc…
Ceramics:
Several Yttrium Barium Copper Oxides (YBa2Cu3O7 YBCO family) which are the most famous high temperature
superconductors. And Magnesium diboride (MgB2), whose
critical temperature is 39K, being the conventional
superconductor with the highest known temperature.
Low Temperature Superconductor:
Become superconductor below the boiling point of LN2 at
77K.
V.
TABLE I. LIST OF SUPERCONDUCTING MATERIALS [1]
High Temperature superconductor:
Become superconductor above the boiling point of LN2 at
77K.
This criterion is used when we want to emphasize whether or
not we can cool the sample with liquid nitrogen (whose
boiling point is 77 K), which is much more feasible than liquid
helium (the alternative to achieve the temperatures needed to
get low temperature superconductors).
LIST OF SUPERCONDUCTING MATERIALS
Material
Pure Metals:
Hc (T)
Tc (K)
Al
Ln
Sn
Pb
Nb
1.2
3.4
3.7
7.2
9.2
Material
NbN
Nb3Ge
105
280
305
803
2060
1933
Tc (K)
Hc (T)
Year
15
23
1.4 X 105
3.7 X 105
1940
1971
C. Based on BCS Theory (John Bardeen, Leon Cooper &
John Schrieffer):
Conventional superconductors:
These are the superconductors which can be fully explained
with the BCS theory or related theories.
Unconventional superconductors:
These are the superconductors which are failed to be explained
using such theories.
This criterion is important, as the BCS theory is explaining the
properties of conventional superconductors since 1957, but on
the other hand there have been no satisfactory theory to
explain fully unconventional superconductors. In most of
cases type I superconductors are conventional, but there are
several exceptions as niobium, which is both conventional and
type II.
13-14 May 2011
Year
1913
1930
Alloys:
Material
La1.85Ba0.15CuO4
YBa2Cu3O7
Bi2Sr2CaCu2O8+x
Ta2Ba2Ca2Cu3O10+x
HgBa2Ca2Cu3O8+x
Ceramics:
Tc (K)
35
93
94
125
150*
* Under pressure
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
Year
1986
1987
1988
1988
1993
National Conference on Recent Trends in Engineering & Technology
VI.
HIGH TEMPERATURE SUPERCONDUCTIVITY
High temperature superconductors (abbreviated high Tc or
HTS) are materials that have a superconducting transition
temperature (Tc) above 30 K (−243.2 °C). From 1960 to 1980,
30 K was thought to be the highest theoretically possible Tc.
The first high-Tc superconductor was discovered in 1986 by
IBM Researchers Karl Muller and Johannes Bednorz, for
which they were awarded the Nobel Prize in Physics in 1987
[8]. Until Fe-based superconductors were discovered in 2008
[9], the term high temperature superconductor was used
interchangeably with cuprate superconductor for compounds
such as bismuth strontium calcium copper oxide (BSCCO)
and yttrium barium copper oxide (YBCO) [10]. Examples of
high-Tc cuprate superconductors include La1.85Ba0.15CuO4, and
YBCO (Yttrium-Barium-Copper-Oxide), which is famous as
the first material to achieve superconductivity above the
boiling point of liquid nitrogen.
"High temperature" has three common definitions in the
context of superconductivity:
1) Above the temperature of 30 K that had historically been
taken as the upper limit allowed by BCS theory. This is
also above the 1973 record of 23 K that had lasted until
copper-oxide materials were discovered in 1986.
2) Having a transition temperature that is a larger fraction of
the Fermi temperature than for conventional
superconductors such as elemental mercury or lead. This
definition encompasses a wider variety of unconventional
superconductors and is used in the context of theoretical
models.
3) Greater than the boiling point of liquid nitrogen (77 K or
−196 °C). This is significant for technological
applications of superconductivity because liquid nitrogen
is a relatively inexpensive and easily handled coolant.
TABLE II. TRANSITION TEMPERATURES OF WELL KNOWN
SUPERCONDUCTORS (BOILING POINT OF LIQUID NITROGEN FOR
COMPARISON) [10]
Material
HgBa2Ca2Cu3Ox
Class
Transition
temperature
(K)
133
Bi2Sr2Ca2Cu3O10
(BSCCO-2223)
110
YBa2Cu3O7
(YBCO-123)
90
Boiling point of
LN2
SmFeAs (O,F)
CeFeAs (O,F)
77
55
41
LaFeAs (O,F)
26
Boiling point of
LH2
Nb3Sn
20
NbTi
10
Nb
9.2
Hg (mercury)
4.2
Copper oxide
superconductors
Iron based
superconductors
18
Metallic low
temperature
superconductors
A. Copper Oxide Superconductors (Cuprates):
Cuprate superconductors are generally considered to be quasitwo-dimensional materials with their superconducting
properties determined by electrons moving within weakly
coupled copper oxide (CuO2) layers. Neighbouring layers
containing ions such as lanthanum, barium, strontium, or other
atoms act to stabilize the structure and dope electrons or holes
on to the copper oxide layers. The undoped 'parent' or 'mother'
compounds are Mott insulators with long range antiferromagnetic order at low enough temperature.
B. Iron based superconductors:
Iron-based superconductors contain layers of iron and a
pnictogen, such as arsenic, phosphorus, or chalcogens. This is
currently the family with the second highest critical
temperature, behind the cuprates. Interest in their
superconducting properties began in 2006 with the discovery
of superconductivity in LaFePO at 4 K and gained much
greater attention in 2008 after the analogous material
LaFeAs(O,F) was found to super conduct at up to 43 K under
pressure.
Figure 4. A small sample of the High Temperature Superconductor
BSCCO-2223.
13-14 May 2011
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
VII. APPLICATIONS OF SUPERCONDUCTIVITY
TABLE III. LARGE SCALE APPLICATIONS OF
SUPERCONDUCTIVITY
Application
Power Cables
Current Limiters
Transformers
Motors/Generators
Magnets for RTD
(Research & Technology
Development ),
Magnetic Energy Storage,
Magnetic Separation,
NMR (Nuclear Magnetic
Resonance) Spectroscopy,
MRI (Magnetic
Resonance Imaging),
Magnetic Levitation
Cavities for Accelerators
Magnetic Bearings
(based on HTS bulk
materials)
Major Technical Features
Higher current densities,
smaller cable diameters, lower
transmission losses
Highly non-linear supernormal conductor transition,
self controlled current
limitation
Higher current densities,
smaller size, lower weight,
lower losses
Higher current densities,
higher magnetic fields, smaller
size, low weight & losses
Higher current densities,
higher and ultra higher
magnetic fields, higher
magnetic field gradients,
smaller size, lower weight,
lower losses, persistent
currents, ultra high temporal
field stabilities, stronger
levitation forces, larger air
gaps
Lower surface resistance,
higher quality factors, higher
microwave-power handling
Higher current densities,
lower losses, stronger
levitation forces, self
controlled auto stable
levitation
Superconducting materials have wide applications in
different field like nuclear magnetic resonance, plasma
research, levitation train and electrical power transmission.
There has been a growing interest in the High temperature
superconductors (HTS) due to their applications as lossless
current leads for magnets, levitation etc. For meaningful
applications of HTS, easy fabrication techniques for its large
scale production are required. The future trend of
superconductivity research is to find materials that can
become superconductors at room temperature. Once this
happens, the whole world of electronics, power and
transmission will be revolutionized.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
T. V. Ramakrishnan, C N R Rao, “Superconductivity Today – An
Elementary Introduction”, Second Edition, Uiversities Press.
John C. Gallop (1990). SQUIDS, the Josephson Effects and
Superconducting Electronics. CRC Press. pp. 3, 20. ISBN 0750300515.
H. K. Onnes (1911). "The resistance of pure mercury at helium
temperatures". Commun. Phys. Lab. Univ. Leiden 12: 120.
F. London and H. London (1935). "The Electromagnetic Equations of
the Supraconductor". Proc. R. Soc. London A 149 (866): 71–88.
V. L. Ginzburg and L.D. Landau (1950). "On the theory of
superconductivity". Zh. Eksp. Teor. Fiz. 20 (1064).
E. Maxwell (1950). "Isotope Effect in the Superconductivity of
Mercury". Phys. Rev. 78 (4): 477.
C. A. Reynolds, B. Serin, W. H. Wright and L. B. Nesbitt (1950).
"Superconductivity of Isotopes of Mercury". Phys. Rev. 78 (4): 487.
J. G. Bednorz and K.A. Mueller (1986). "Possible high TC
superconductivity in the Ba-La-Cu-O system". Z. Phys. B64 (2): 189–
193.
Ren, Zhi-An; Che, Guang-Can; Dong, Xiao-Li; Yang, Jie; Lu, Wei; Yi,
Wei; Shen, Xiao-Li; Li, Zheng-Cai et al. (2008). "Superconductivity
and phase diagram in iron-based arsenic-oxides ReFeAsO1−δ (Re =
rare-earth metal) without fluorine doping". EPL (Europhysics Letters)
83: 17002.
Anthony Leggett (2006). "What DO we know about high Tc?”, Nature
Physics 2: 134.
L. R. Lawrence et al: "High Temperature Superconductivity: The
Products and their Benefits" (2002) Bob Lawrence & Associates, Inc.
CONCLUSION:
The basic facts about Superconductivity are:
 Resistivity goes to zero below the critical temperature Tc
(the most sensitive measurements imply R < 10-25 Ω).
 Many different materials show superconductivity.
 Critical Temperature (Tc) values range from a few mK up
to 160 K.
 Superconductors expel flux (the Meissner effect) and act
as perfect diamagnets.
 Superconductivity is destroyed by a critical magnetic field
Bc.
 Specific heat, infrared absorption, tunneling etc... all
imply that there is an energy gap associated with
superconductivity
13-14 May 2011
B.V.M. Engineering College, V.V.Nagar,Gujarat,India