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Discoveries of Superconductivity

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Rob Shalloo

on 15 October 2013

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Transcript of Discoveries of Superconductivity

www.esa.int
Cork, Ireland
www.ucc.ie
University College Cork
Discoveries of Superconductivity
Robert Shalloo
Objectives
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
March 7, 2013
What is superconductivity?
Discovery of superconductivity
Meissner Effect
Ginzburg–Landau Theory
BCS Theory
Superconductors in magnetic fields
High Temperature Superconductivity
Quantum mechanical phenomenon characterized by two properties:
Zero electrical resistance
Expulsion of magnetic fields
What is Superconductivity
teachers.web.cern.ch
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
www.nobelprize.org

Heike Kamerlingh Onnes used the Hampson–Linde cycle to become the first person to liquify Helium on July 10th 1908.


On April 8, 1911, Kamerlingh Onnes found that at 4.2 K the resistance in a solid mercury wire immersed in liquid helium suddenly vanished

Onnes' lab dubbed "coldest place on earth"
Discovery
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
www.superconductor.org
1908
1913
1933
1957
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
Bardeen Cooper Schrieffer Theory
The Meissner Effect
1911
Onnes
1972
Bardeen, Cooper, Schrieffer
1986
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
High Temperature Superconductivity
The ejection of the magnetic field from a superconductor during its transition to the superconducting state.

Can be related conceptually to Faraday and Lenz's law
Walther Meissner
Robert Ochsenfeld
Persistent currents set up which act to oppose the applied magnetic field within a distance known as the London Penetration Depth. Thus the material has essentially infinite conductivity.
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
Type I Superconductors in
Superconductors posses a critical magnetic field, above which superconductivity is destroyed
hyperphysics.phy-astr.gsu.edu
simpliphy.wordpress.com
Critical magnetic field and critical temperature can be viewed as energy required to reduce the band gap sufficiently to break cooper pairs
As electrons move through the solid they cause lattice deformations, creating an area of positive charge which attracts a second electron. This attractive electron phonon interaction creates whats called a cooper pair.

Cooper pairs have less energy than electrons on their own.This leads to an energy band gap in the material

Breaking these pairs requires energy greater than the band gap


Penetration depth and London equation emerge as consequences of the theory. Thus the Meissner Effect is obtained in a natural way.
lrrpublic.cli.det.nsw.edu.au
hyperphysics.phy-astr.gsu.edu
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
Bardeen Cooper Schrieffer Theory
(CGS)
=0
Metallic compounds and alloys
After critical field is reached, magnetic field can penetrate in discrete units called fluxons.
Gradual tranistion to superconducting state
www.nobelprize.org
1950
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
Ginzburg–Landau Theory
Phenomenological model which could describe type-I superconductors without examining their microscopic properties.
Predicted type-II superconductors
Ginzburg
Landau
www.nobelprize.org
en.wikipedia.org
2003
Abrikosov, Ginzburg, Leggett
Alexei Abrikosov
Robert Shalloo
hyperphysics.phy-astr.gsu.edu
Bednorz, Müller
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
High Temperature Superconductivity
Experimental Discovery
www.nobelprize.org
J. Georg Bednorz
K. Alex Müller
www.nobelprize.org
Two IBM researchers working in Switzerland created a brittle ceramic compound that had the highest critical temperature then known: 30 K

For this they were awarded the Nobel Prize the following year.


The result was strange as ceramics are usually good insulators
Type I (Soft) :
Posses extremely low critical temperatures
Sharp transition to superconducting state
Type II (Hard) :
Posses higher critical temperatures
Gradual transition to superconducting state
Magnetic Fields
2013
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
Today
100 years since the first Nobel Prize was awarded for Superconductivity
Still searching for superconductors with yet higher critical temperatures.
Focus on applications:
Public transportation systems
Locking spacecraft for docking
Cable-less elevators
Energy storage
Electronics
Physics 141A
Spring 2013
Robert Shalloo
UC Berkeley
Thank you! Questions
Beginnings
He predicted that at low temperatures pure metals would become perfect electromagnetic conductors
James Dewar initiated research into electrical resistance at low temperatures
To test his theories low temperatures were needed
www.wikipedia.org
Hampson Linde Cycle:
Indepdantly patented in 1895, uses the Joule-Thompson effect to cool gases (air) by letting the gas molecules expand freely against the atmosphere.
Band Gap:
An energy range in a solid where no electron states can exist
Full transcript