Superconductivity is a phenomenon that occurs in certain materials below a critical temperature where they show zero electrical resistance. It was discovered in 1911 by Heike Kamerlingh Onnes who found that mercury's resistivity disappeared below 4K. Superconductors expel magnetic fields, known as the Meissner effect. An experiment is described where a ceramic disk made of yttrium-barium-copper oxide is cooled below its critical temperature using liquid nitrogen, causing it to become a superconductor and levitate a small magnet due to persistent electric currents. Theories like the BCS theory and London theory were developed to explain the microscopic mechanisms of superconductivity.

2. SUPERCONDUCTIVITY
 is the phenomenon of exactly zero electrical resistance.
 expulsion of magnetic fields occurring in certain materials when cooled
below a characteristic critical temperature .
 It is a quantum mechanical phenomenon .
 It was discovered by Heike Kammerlingh Onnes .
 He discovered that the resistivity of mercury absolutely disappears
at temperatures below about 4K.
 It is characterized by Meissner effect ,the complete ejections of magnetic
fields lines from the interior of superconductor as it transitions into a
superconducting state.
 An induced current in an ordinary metal ring would decay rapidly from the
dissipation of ordinary resistance, but superconducting rings had exhibited a
decay constant of over a billion years!

3. AN EXPERIMENT TO DESCRIBE
SUPERCONDUCTIVITY
 All you have to do is :-
 Get “Liquid Nitrogen”, “A Petri dish” , “A ceramic disk made of Yttrium-
Barium-Copper oxide", "small magnet", "some load to keep the ceramic”.
 Take the ceramic disk and keep it over load to make a certain height. Now
pour the liquid nitrogen over it .
 liquid nitrogen will cool down the ceramic to 0K(-273 degree Celsius)
 After reaching the absolute zero or nearer to that ,the ceramic disk will
become a superconductor .
 A magnet will levitate over the superconductor( like an anti gravity ) .
 Persistent electric current will flow on the surface of the superconductor
,acting to exclude the magnetic field of the magnet(Faraday’s law of
induction) .this current effectively forms an electromagnet that repels the
magnet, characterizing Meissner effect
his is a video on superconductivity . Double Click to

4. Terms
 Liquid nitrogen :- Liquid nitrogen is nitrogen in a liquid state at an extremely
low temperature. It is produced industrially by fractional distillation of liquid
air . It is used for cooling a high-temperature superconductor to a
temperature sufficient to achieve superconductivity .
 Ceramic(Yttrium- Barium-Copper-Oxide):-
Yttrium barium copper oxide, often abbreviated YBCO, is
a crystalline chemical compound with the formula YBa2Cu3O7. This material,
a famous "high-temperature superconductor", achieved prominence because
it was the first material to achieve superconductivity above the boiling point
(77 K) of liquid nitrogen.
Liquid
nitrogen
Yttrium barium
copper oxide

5. • Meissner effect :- The Meissner effect is an expulsion of a magnetic
field from a superconductor during its transition to the superconducting
state.
Diagram of the Meissner effect. Magnetic field lines,
represented as arrows, are excluded from a
superconductor when it is below its critical
temperature.

6.  When a superconductor is placed in a weak external magnetic field,
the field penetrates the superconductor only at a small distance,
called the London penetration depth, decaying exponentially to
zero within the bulk of the material.
 This is called the Meissner effect, and is a defining characteristic of
superconductivity.
 For most superconductors, the London penetration depth is on the
order of 100 nm.

7. EXPLANATION
 The electrical resistivity of the metallic conductor decreases gradually
as temperature is lowered . In ordinary conductors , such as copper or
silver ,this decrease is limited by impurities and other defects .
 Even near absolute zero, a real sample of a normal conductor shows
some resistance. In a superconductor, the resistance drops abruptly to
zero when the material is cooled below its critical temperature.
 In 1986, it was discovered that some cuprate-
perovskite ceramic materials have a critical temperature above 90
K (−183 °C). Such a high transition temperature is theoretically
impossible for a conventional superconductor, leading the materials to
be termed high temperature superconductor

8. Phonon
 phonon, a unit of vibrational energy that arises from
oscillating atoms within a crystal. Any solid crystal, such as
ordinary table salt (sodium chloride), consists of atoms bound into a
specific repeating three-dimensional spatial pattern called a lattice.

9. Liquid nitrogen and superconductivity
 Liquid nitrogen boils at 77 K, facilitating many
experiments and applications that are less practical at
lower temperatures. In conventional superconductors,
electrons are held together in pairs by an attraction
mediated by lattice phonons. The best available model of
high-temperature superconductivity is still somewhat
crude. There is a hypothesis that electron pairing in high-
temperature superconductors is mediated by short-range
spin waves known as paramagnons.

10. PHASE TRANSITION
 In superconducting materials, the phase transition appear when the
temperature T is lowered below a critical temperature Tc. The value of this
critical temperature varies from material to material.
 Superconductors usually have critical temperatures below 20 K
(down to less than 1 K).
 Cuprate superconductors can have much higher critical temperatures.
Mercury-based cuprates have been found with critical temperatures in
excess of 130 K.

11.  Superconductivity was discovered on April 8, 1911 by Heike Kamerlingh
Onnes, who was studying the resistance of
solid mercury at cryogenic temperatures using the recently-
produced liquid helium as a refrigerant. At the temperature of 4.2 K, he
observed that the resistance abruptly disappeared. In the same
experiment, he also observed the superfluid transition of helium at 2.2 K,
without recognizing its significance. (The precise date and circumstances
of the discovery were only reconstructed a century later, when Onnes's
notebook was found.) In subsequent decades, superconductivity was
observed 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.

12.  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.
 In 1950, the phenomenological Ginzburg-Landau theory of
superconductivity was devised by Landau and Ginzburg . 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.
 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.
 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.

13. THEORIES OF SUPERCONDUCTIVITY
 Ginzburg-Landau theory (1950)
Ginzburg–Landau theory, named after Vitaly Lazarevich Ginzburg and Lev Landau, is
a mathematical theory used to model superconductivity. It does not purport to explain
the microscopic mechanisms giving rise to superconductivity. Instead, it examines
the macroscopic properties of a superconductor.
 BCS theory(1957)
proposed by Bardeen, Cooper, and Schrieffer (BCS) in 1957, is the first microscopic
theory of superconductivity since its discovery in 1911. The theory
describes superconductivity as a
microscopic effect caused by a condensation of pairs
of electrons into a boson-like state.(Bosons are one of
the two fundamental classes of subatomic particles,)

14. • LONDON THEORY(1935)
The first phenomenological theory of superconductivity was London theory. It
was put forward by the brothers Fritz and Heinz London in 1935, shortly after
the discovery that magnetic fields are expelled from superconductors. A major
triumph of the equations of this theory is their ability to explain the Meissner
effect.

15. Superconductor
classification
Criteria to classify superconductor are:--
 By their response to a magnetic field: they can be Type I, meaning
they have a single critical field, above which all superconductivity is
lost; or they can be Type II, meaning they have two critical fields,
between which they allow partial penetration of the magnetic field.
 By the theory to explain them: they can be conventional (if they are
explained by the BCS theory or its derivatives) or unconventional (if
not).
 By their critical temperature: they can be high temperature (generally
considered if they reach the superconducting state just cooling them
with liquid nitrogen, that is, if Tc > 77 K), or low temperature (generally if
they need other techniques to be cooled under their critical
temperature).
 By material: they can be chemical
elements(as mercury or lead), alloys (as niobium-
titanium or germanium-niobium or niobium
nitride),ceramics (as YBCO or the magnesium diboride), or organic
superconductors (as fullerenes or carbon nanotubes, though these
examples technically might be included among the chemical elements
as they are composed entirely of carbon).

16. APPLICATION OF
SUPERCONDUCTOR
Superconducting magnets are some of the most
powerful electromagnets known.
They are used in:----
 MRI / NMR machines,
 mass spectrometers
 beam-steering magnets used in particle accelerators.
 digital circuits based on rapid single flux quantum Technology
and RF and microwave filters for mobile phone base stations.
 Superconductors are used to build Josephson junctions
which are the building blocks of SQUIDs(superconducting
quantum interference devices)
Promising future applications include
 high-performance smart grid.
 electric power transmission,
 transformers,
 power storage devices,
 electric motors
 Nanotubes

17. Nobel Prizes for superconductivity
 Heike Kamerlingh Onnes (1913), "for his investigations on the properties
of matter at low temperatures which led, inter alia, to the production of
liquid helium"
 John Bardeen, Leon N. Cooper, and J. Robert Schrieffer (1972), "for their
jointly developed theory of superconductivity, usually called the BCS-
theory"
 Leo Esaki, Ivar Giaever, and Brian D. Josephson (1973), "for their
experimental discoveries regarding tunneling phenomena in
semiconductors and superconductors, respectively," and "for his
theoretical predictions of the properties of a supercurrent through a
tunnel barrier, in particular those phenomena which are generally
known as the Josephson effects"
 Georg Bednorz and Alex K. Muller (1987), "for their important break-
through in the discovery of superconductivity in ceramic materials"
 Alexei A. Abrikosov, Vitaly L. Ginzburg, and Anthony J. Leggett (2003),
"for pioneering contributions to the theory of superconductors and
superfluids"

18. MADE BY – Aditya Shinde
DPS Raipur
thanks