Superconductors: Simplicity in Motion

1
Superconductors Simplicity in Motion
2
Kelvin Temperature Scale
100oC 373 K
0oC 273 K
High Temperature Superconductors
-145oC 138 K
Air (Nitrogen) liquifies
77 K
Helium liquifies
4 K
0 K All motion ceases
3
Superconductors A different phase of matter
Phases of atoms and molecules
0 K
Gas or Liquid
Solid (a lattice)
Hot
Electron Solid ?
Metals (electrons can move in the solid)
Phases of electrons in solids
4
Superconductors A different phase of matter
Phases of atoms and molecules
0 K
Gas or Liquid
Solid (a lattice)
Hot
Electron Solid ?
Metals (electrons can move in the solid)
Phases of electrons in solids
5
The Discovery
Resistance of Mercury Onnes (1911)
Normal Metal
Resistance
Mercury
4 K
Temperature
6
History of Superconductivity
Meissner Effect (1933)
Bardeen, Cooper, Schrieffer Theory (1957)
High Temperature Superconductors (1985)
Müller Bednorz
7
Superconducting Elements
Ambient Pressure High Pressure
8
Metals Normal Conductors
electron
VOltage
creates a hill for
Voltage
electrons
9
Metals Normal Conductors
electron
VOltage
creates a hill for
Voltage
electrons
for electrons to reach the bottom is like the
Average time
resistance.
10
Resistivity
11
Phases of Water
Pressure
Pressure at sea level
Liquid
iCE
vAPOR
Pressure on On Mt Everest
Temperature
100OC (373K)
0OC (273K)
12
Minimum Free Energy Boiling water with a pump
Liquid
Pressure
Liquid
iCE
vAPOR
Temperature
13
Minimum Free Energy Boiling water with a pump
Liquid
Pressure
Liquid
iCE
vAPOR
Temperature
14
Minimum Free Energy Boiling water with a pump
Liquid
Pressure

Liquid
vAPOR
iCE
vAPOR
Temperature
15
Minimum Free Energy Boiling water with a pump
Pressure
vAPOR
Liquid
vAPOR
iCE
vAPOR
Temperature
16
Minimum Free Energy Boiling water with a pump
Pressure
vAPOR
Liquid
vAPOR
iCE
vAPOR
Super-heated Water
Temperature
17
Minimum Free Energy Boiling water with a pump
Pressure
vAPOR
Liquid
vAPOR
iCE
vAPOR
Temperature
18
Magnets Another State of Matter
Madame Curie
Energy
TCurie
Temperature
Magnetization
M 0, no net alignment
19
Magnets Another State of Matter
TCurie
Temperature
M 0, Local alignment, but no net alignment
20
Magnets Another State of Matter
T TCurie
TCurie
Temperature
M 0, Local alignment, but no net alignment
21
Magnets Another State of Matter
T lt TCurie
TCurie
Temperature
M gt 0, Net alignment
22
Magnets Another State of Matter
Symmetry Breaking
T lt TCurie
TCurie
Temperature
M gt 0, Net alignment
23
Magnets Another State of Matter
T lt TCurie
TCurie
Temperature
M gt 0, Net alignment
24
Superconducting Phase Diagram
Critical Field
Normal Metal
Magnetic Field
Critical Temperature
Superconductor
Superconducting magnet being built at U of
Illinois
Temperature
25
Superconducting Phase Diagram
Critical Field
Normal Metal
Magnetic Quenching (oops)
Magnetic Field
Critical Temperature
Superconductor
Superconducting magnet being built at U of
Illinois
Temperature
26
Superconducting Free Energy

• The electrons in a superconductor behave as a
  single particle.
• In quantum mechanics particles are represented
  by waves.
• Waves have two parts.

27
Superconducting Free Energy
Free Energy
TC
Temperature
28
Superconducting Free Energy
Free Energy
Free Energy
TC
Temperature
29
Superconducting Free Energy
Free Energy
Free Energy
TC
Temperature
30
Superconducting Free Energy
Free Energy
TC
Temperature
31
Superconducting Free Energy
Free Energy
TC
Temperature
32
Superconducting Free Energy
Free Energy
TC
Temperature
33
Superconducting Free Energy
Free Energy
TC
Temperature
Top View
34
Particle Spin
Fermions Electrons Protons Neutrons
Bosons Photons (light) Phonons
(vibrations) Cooper pairs
Integer Spin
1/2 Integer Spin
35
Fermions and Bosons
Fermions
Exclusion Principle.
do not.
obey the
Pauli
Bosons
36
Fermions and Bosons
Data From Randy Hulet at Rice
Fermions Lithium 7
Bosons Lithium 6
Fermions
Exclusion Principle.
do not.
obey the
Pauli
Bosons
37
How to make Bosons out of Electrons
1/2
1/2
0

-
38
Cooper Pairs Can alikes attract?
Two electrons in a Cooper Pair The lattice is
slow and heavy, but the electrons are fast The
attraction between electrons depends on the mass
of the ion.
39
Magnetic Properties of Supercondcutors
Magnets can repel each other, but you cant
float two magnets
Changing Magnetic Field Electric Field
40
High magnetic fields orIf you cant beat em
join em
Critical Field
Normal Metal
Magnetic Field
Critical Temperature
Pure Superconductor
Temperature
41
High magnetic fields orIf you cant beat em
join em
Critical Fields
Normal Metal
Vortex State
Magnetic Field
Critical Temperature
Pure Superconductor
Temperature
42
The Vortex State
Higher Magnetic Field
43

• Superconductors are a phase of matter where
  current flows without resistance.
• Phase changes occur when the energy of two
  phases are equal.
• Superconductors behave as if the current were
  carried by a single particle.
• Electrons are Fermions Cooper Pairs are Bosons.
• Superconductors are used in many devices.
• Superconductivity is a low-temperature
  phenomenon.