Graduate Lecture Series 29 June – 3 July, 2009 Prof Ngee-Pong Chang

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

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

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

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 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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