The document discusses the BCS theory of superconductivity proposed by Bardeen, Cooper, and Schrieffer. The key points are: 1) The BCS theory successfully explains the microscopic origin of superconductivity as arising from the condensation of electron pairs known as Cooper pairs into a boson-like state below a critical temperature. 2) Cooper pairs form when an attractive interaction binds two electrons with opposite spin and momentum due to an exchange of phonons in the metal lattice. 3) The BCS theory can fully explain conventional superconductivity in type I superconductors but has limitations for type II superconductors.

1. BBardeenardeen
CCooperooper
SSchriefferchrieffer
Theory ofTheory of
SuperconductivitySuperconductivity
Presented toPresented to
Prof. Dr. Jameel Un NabiProf. Dr. Jameel Un Nabi
Presented ByPresented By
Assad Ur RehmanAssad Ur Rehman
ES-1717ES-1717
Faculty Of Engineering SciencesFaculty Of Engineering Sciences
Ghulam Ishaq Khan Institute Of EngineeringGhulam Ishaq Khan Institute Of Engineering
Sciences & TechnoogySciences & Technoogy

2. ContentsContents
 Introduction.Introduction.
 Theories.Theories.
 Cooper Pairs.Cooper Pairs.
 BCS Theory.BCS Theory.
 Drawbacks.Drawbacks.
 Summary.Summary.

3. IntroductionIntroduction
 BCS successfully and completely explains theBCS successfully and completely explains the
microscopic origin of super conductivity.microscopic origin of super conductivity.
 It is a mean filed theory.It is a mean filed theory.
 Applicable to conventional super conductors only.Applicable to conventional super conductors only.

4. SuperconductivitySuperconductivity
 Superconductivity is a phenomenon displayed bySuperconductivity is a phenomenon displayed by
certain conductors that demonstrate no resistance tocertain conductors that demonstrate no resistance to
the flow of an electric current. Superconductors alsothe flow of an electric current. Superconductors also
exhibit strong diamagnetism; that is, they are repelledexhibit strong diamagnetism; that is, they are repelled
by magnetic fields. Superconductivity is manifestedby magnetic fields. Superconductivity is manifested
only below a certain critical temperatureonly below a certain critical temperature TTc and ac and a
critical magnetic fieldcritical magnetic field HHc, which vary with thec, which vary with the
material used. Before 1986, the highest Tc was 23.2material used. Before 1986, the highest Tc was 23.2
K (-249.8°C, -417.6° F) in niobium-germaniumK (-249.8°C, -417.6° F) in niobium-germanium
compounds.compounds.

5. SuperconductivitySuperconductivity
 Discovered byDiscovered by Kamerlingh OnnesKamerlingh Onnes inin
1911 during first low temperature1911 during first low temperature
measurements to liquefy helium.measurements to liquefy helium.
 Whilst measuring the resistivity ofWhilst measuring the resistivity of
““pure” Hg he noticed that thepure” Hg he noticed that the
electrical resistance dropped to zeroelectrical resistance dropped to zero
at 4.2K.at 4.2K.
 In 1912 he found that the resistiveIn 1912 he found that the resistive
state is restored in a magnetic fieldstate is restored in a magnetic field
or temperatures.or temperatures.
19131913

6. TypeType II SuperconductorsSuperconductors
 In type Type I superconductors transition from normalIn type Type I superconductors transition from normal
state to superconducting state occurs instantly i.e. atstate to superconducting state occurs instantly i.e. at
exactly it's critical/transition temperature Tc like pureexactly it's critical/transition temperature Tc like pure
metals mercury, lead and aluminum.metals mercury, lead and aluminum.

7. TypeType IIII SuperconductorsSuperconductors
In Type II superconductors transition from a
normal state to a superconducting state occurs
"slowly" i.e. as temperature decreases from it's
critical temperature superconducting
properties increase. Examples of type II
superconductors are alloys and ceramic like
niobium-titanium and niobium-tin.

8. TheoriesTheories
 Drude Model of Metals failed to explain the Drude Model of Metals failed to explain the
superconductivity.superconductivity.
 London Equations explained superconductivity with London Equations explained superconductivity with
some limitations.some limitations.
 Giznberg Landaue proposed a macroscopic model Giznberg Landaue proposed a macroscopic model
based on thermodynamic parameters.based on thermodynamic parameters.

9. BCS TheoryBCS Theory
 Bardeen-Cooper-Schrieffer theory ofBardeen-Cooper-Schrieffer theory of
superconductivity explains the origin ofsuperconductivity explains the origin of
superconductivity as effect caused by thesuperconductivity as effect caused by the
condensation ofcondensation of Cooper-pairsCooper-pairs into a boson-likeinto a boson-like
state[2].state[2].
19721972

10. Cooper PairsCooper Pairs
 In condensed matter physics, aIn condensed matter physics, a Cooper pairCooper pair oror
BCSBCS pairpair is ais a pairpair of electrons (or other fermions)of electrons (or other fermions)
bound together at low temperatures in a certainbound together at low temperatures in a certain
manner first described in 1956 by American physicistmanner first described in 1956 by American physicist
LeonLeon Cooper[3]Cooper[3]..
 The physical idea is that, the first electron polarizesThe physical idea is that, the first electron polarizes
the medium bythe medium by attracting positive ions &attracting positive ions &
 These excess positive ions in turn attract the secondThese excess positive ions in turn attract the second
electron (with opposite spin and momenta), giving anelectron (with opposite spin and momenta), giving an
effective attractive interaction between the electrons.effective attractive interaction between the electrons.

11. Cooper PairsCooper Pairs

12. Cooper PairsCooper Pairs

13. DrawbacksDrawbacks
 Does not explain the superconductivity of Type II
superconductors.
 Valid at low temperatures only.Valid at low temperatures only.
 Does not predict which materials may be
superconductors.

14. SummarySummary
 BCS successfully explains the microscopic origin ofBCS successfully explains the microscopic origin of
superconductivity.superconductivity.
 An attractive interaction between electrons will resultAn attractive interaction between electrons will result
in forming bound Cooper pairs.in forming bound Cooper pairs.
 BCS can only explain superconductivity in type IBCS can only explain superconductivity in type I
superconductors only.superconductors only.

15. ReferencesReferences
1.1.Dirk (2007) Freezing physics, Heike Kamerlingh Onnes and the quest for cold, Edita,
Amsterdam.
2. Phys. Rev. 108, 1175 (1957)
3.3.Cooper, Leon N. (1956). "Bound electron pairs in a degenerate Fermi gas". Physical
Review. 104 (4): 1189–1190.

16. THANK YOUTHANK YOU