graduate lecture series 29 june – 3 july, 2009 prof ngee-pong chang
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Graduate Lecture Series29 June – 3 July, 2009
Prof Ngee-Pong Chang
Lecture 5
SuperconductivityFlux Quantization
&SQUID
Kammerlingh Onnes 1853-1926
On the Sudden Rate at Which the Resistance of Mercury Disappears
Communications of the Leiden Laboratory, 1911
Onnes-Holst measurement of Hg resistance
Meissner Effect
1933
Walther Meissner1882 - 1974
Robert Ochsenfeld
Inside sphere
Superconductivity
Drude’s Theory of Conductivity
Perfect conductorLimit
London’s Equations
London’s Equation
London’s Equation
SuperconductorIs better than
perfect conductor
London Equations
Fritz London
Proc Roy Soc A149, 71, 1935
Maxwell’s Equations for Superconductor
http://web.mit.edu/6.763/www/FT03/Lectures/Lecture17.pdf#search=%22superconducting%20phase%20diagram%20lecture%22
http://web.mit.edu/6.763/www/FT03/Lectures/Lecture17.pdf#search=%22superconducting%20phase%20diagram%20lecture%22
John Bardeen Leon Cooper John R. Schrieffer
BCS Theory of Superconductivity
Phys.Rev.108, 1175 (1957)
Superconductor Charge Density
In Absence of Magnetic Field
Cooper Pair has zero momentum
In absence of Magnetic Field
momentum
In presence of Magnetic Field
momentum
Cooper Pair with zero momentum
In the Presence of Magnetic Field
Superconducting Current
charge density is constant
phase depends on vector potential
Superconducting current
Quantization of Flux
Deep inside
Deep inside
fluxoid
Fluxoid Quantization
B.Deaver & W. Fairbank
Phys Rev Lett 7, 43 (1961)
Brian D. Josephson
1940 -
I II
Vo
I II
Vo
Josephson Current
D.C. Josephson effect
Anderson & Rowell experiment, 1963
For V ≠ 0 , JDC = 0
For V = 0 , JDC = Jo sin δo P.W. Anderson
A.C. Josephson Current
A.C. Josephson Current
PQ
b
a
Ca
Cb
Coupled Josephson Junctions in an external magnetic field
SQUID
PQ
b
a
Ca
Cb
SQUID current for general Flux
SQUID
SQUID Biomagnetic Device
Look to the Galaxies
Is terrestrial physics different than celestial ?
10-12 August, 2005
Nanyang Technological UniversityNational University of Singapore
Biopolis, A*STAR
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