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5/26/2018 Basic Superconductivity
1/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
SuperconductivityProfessor Ted Forgan
Exploring the world of Low Temperatures and Quantum effectshttp://www.phy
sics.ubc.ca/~outreach/phys420/p420_
96/bruce/ybc
o.html
5/26/2018 Basic Superconductivity
2/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Superconductivity
how do we get to low temperatures?
why does it happen?
what use is it?
what is superconductivity?
5/26/2018 Basic Superconductivity
3/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
300 K
200 K
100 K
0 K
liquid N2
77 K
liquid He
4.2 K
hot day
27 C
Dewar (vacuum) flask
5/26/2018 Basic Superconductivity
4/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Kamerlingh OnnesLiquefied He 1908
5/26/2018 Basic Superconductivity
5/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Temperature
Tc= 4.2 K
Resistanceof pure
mercury
Kamerlingh Onnes:Superconductivity 1911
http://www.nobel.se/physics/la
ureates/1913/onnes-bio.h
tml
5/26/2018 Basic Superconductivity
6/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
-all previous theories
were unable to describe
Superconductivity!
Thats because it
involved new physics:
Quantum Mechanics
5/26/2018 Basic Superconductivity
7/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
The Meissner (and Ochsenfeld) Effect
superconductors push out magnetic fields
- and keep them outwith constantly- flowingresistance-less currents
this diamagnetic property is more fundamental than zero resistance
T> Tc T< Tc
http:/
/www.p
hysics.u
bc.c
a/~ou
treac
h/phys4
20/p420
_96/bruce
/ybco.h
tm
l
5/26/2018 Basic Superconductivity
8/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Persistent Currents
SN
SN
currents flow in loops under the poles
-and repel the magnet as ifthere were an image magnet
underneath: N to N and S to S!
superconducting plate
B
supercurrent can also flowaround a ring
giving a magnetic field Bthat never dies away
5/26/2018 Basic Superconductivity
9/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Circulating Super-currents are stablebecause of Quantum effects
large B small B
small Ilarge I
?
de Broglie:
= h / pCurrents form stable wave patterns:
the numberof wavelengths cannot decaysmoothly to zero
5/26/2018 Basic Superconductivity
10/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Levitation with High-Tc Superconductors
A kg or so of fish bowl
up to 202 kg of sumo wrestler!
www.istec.or.jp
5/26/2018 Basic Superconductivity
11/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
More levitation: Yogic Flying
a trick of thecamera?
orsuperconductivity!!??
TranscendentalMeditation?
SN SN SN
ht
tp://www.vedicobservato
ry.org/A7YogicFlying.html
5/26/2018 Basic Superconductivity
12/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
More levitation: Flying Frog
water is slightlyrepelled bymagnetic fields. This supportsa frog or a strawberry - in ahighmagnetic field gradient
http://www.hfml.kun.nl/
5/26/2018 Basic Superconductivity
13/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Georg Bednorzand Alex Muller
received the
Nobel Prize 1987for discovery ofthe first of thecopper-oxide
superconductors
this is how itwas announced
http://www.phys.ntnu.no/brukdef/prosjek
ter/super/Profiles/bednm
ull.jpg
5/26/2018 Basic Superconductivity
14/32 Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Possible High Tcsuperconductivity inthe Ba La Cu O
system
resistivity
(cm)
Temperature( K)
35 K
10 K
Their sample at first becamemoreresistive as it cooled!
At 35 K, when the sample was5000 x more resistive than copper,
the resistance began to fall
Only by 10 Khad the resistancefallen to (possibly) zero !
5/26/2018 Basic Superconductivity
15/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
93 K !
77 Kliquid
nitrogen
5/26/2018 Basic Superconductivity
16/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
1910 1930 1950 1970 1975 1980 19901985 20001995 2005
HgPb Nb
NbO
NbNV3Sn
NbAlSi
Nb3Sn
Ba(Pb,Bi)O3
organic materials
NbGe3Ba(K,Bi)O3
Doped buckyballsA3C60
MgB239K
Liquid N2
Liquid He0-
10-
70-
30-
20-
120-
60-
50-
40-
110-
90-
100-
80-
130-
140 -
150- Temperature(K)
conventionalsuperconductors
(La,Ba)CuOBednorz and Muller
TlBaCaCuO
Bi2Sr2Ca2Cu3Ox
HgBaCaCuO
pressur e
~ 155K
High temperaturecuprate
superconductorsYBa2Cu3O7-d
pressur e
5/26/2018 Basic Superconductivity
17/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
The crystal structures of High-Tcsuperconducting materials all have
copper-oxide CuO2layers
Is a room-temperaturesuperconductor out there
waiting to be discovered ??
Have we reachedthe maximum
possible Tcin thisclass of materials?
We are still notsure exactly whythis is important!
5/26/2018 Basic Superconductivity
18/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
John Bardeen, Leon Cooper and Bob Schrieffer
B. C. S.Nobel Prize 1972 for their theory of 1957 whichexplained conventional superconductors: nearly 50years after their discovery by Kamerlingh Onnes!
http://sup
erconductors.org/history
.htm#resist
5/26/2018 Basic Superconductivity
19/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Cooper Pairs
each electron in a pair does its own thing
(as the Pauli Exclusion Principle says it must)
but the CENTRES OF MASS of allthe pairs do exactly the SAME thing
(all at rest, or all carrying a steady current)
and how can weprovethey travel inpairs ?
but what force holds the electrons together?
5/26/2018 Basic Superconductivity
20/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
The BCS attractive mechanismis due to electrons
slightly deformingthe crystal lattice
- but we can visualise it asthe sagging mattress
effect!
A theoretician would describe thisattraction as due to exchange of
virtual phonons
RandySimon,AndySmith,Superconductors
5/26/2018 Basic Superconductivity
21/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
The Quantum of magnetic flux o
large flux
small Ilarge I
=h / p
o = h/2e
small flux
=nowith n= 8
n= 4
= nowith n= 4
n= 8
2e
- because the electrons go round in pairs!
5/26/2018 Basic Superconductivity
22/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Measurement ofthe Quantum of
magnetic flux oin YBCO by the
Birmingham Group
YBCO ring
blutak!
flux detector
calibration coil
5/26/2018 Basic Superconductivity
23/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Millikan-style results on flux quantisation
flux jump
h / 2e
-so electrons are paired in High-Tcmaterials just like BCS onesbut WHAT attracts them?
5/26/2018 Basic Superconductivity
24/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Flux lines in superconductors
For some superconductors, called Type II,the Meissner effect is not complete, andhigh enough magnetic fields can enter
each carries a fluxof o= h /2e
as flux lines
field lines run from a magnet into adisk of superconductor which is
suspended swinging under the magnet
://w
ww.fys.uio.no/super/levit
ation/
B h d d Ph G
5/26/2018 Basic Superconductivity
25/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
- in Grenoble
ESRF: X-raysILL: neutrons
the most powerfulresearch reactor
in the world
We can detect flux lines with neutrons
Bi i h C d d M Ph i G
5/26/2018 Basic Superconductivity
26/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
using neutron diffraction
Bi i h C d d M Ph i G
5/26/2018 Basic Superconductivity
27/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Typical results from a low-Tcmaterial
Looking at a reactor through a flux line latticeis like looking at a street lamp through an umbrella
niobium 0.2 T low resolution niobium 0.2 T high resolution
Bi i h C d d M tt Ph i G
5/26/2018 Basic Superconductivity
28/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Typical results from a high-Tcmaterial
SQUARE not triangular patterns!These data (published 2004) tell us about electron pairing in YBCO
YBCO B= 1 T YBCO B= 11 T
Bi i h C d d M tt Ph i G
5/26/2018 Basic Superconductivity
29/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Superconducting QuantumInterference Devicescan
measure tiny fields such asthose due to currents flowing
in your heart muscle
The quantum of flux, o= h/ 2e,has the tiny value 2 x 10-15T.m2
The application of QuantumMechanics to measure tinymagnetic fields: SQUIDs
This is one millionth of the fluxdue to the earths field through
the hole in a polomint!
Bi i h C d d M tt Ph i G
5/26/2018 Basic Superconductivity
30/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
The dream - Tomorrows Superconducting World
350 mphlevitated
Intercitytrains
Underground rapid transit:Heathrow to Gatwick in 10
minutes
Computing:1000 times fastersupercomputers
Cargo-carrying
submarines,all-electricUS Navy
Energy Saving:power lineselectric motorstransformers
MedicalDiagnostics:MagneticResonanceImagingSQUID:
Brain activity
Heart function
Information Technology:much faster, wider band
communications
magnetically
launchedspaceshuttle
Bi i h C d d M tt Ph i G
5/26/2018 Basic Superconductivity
31/32
Physics Summer School: Superconductivity Ted Forgan
Birmingham Condensed Matter Physics Group
Some of these dreams are already reality
Japanese levitating train hassuperconducting magnets onboard
Superconducting power cableinstalled in Denmark
SQUIDmeasure-ment ofneuro-
magneticsignals
(nuclear) magneticresonance imaging of thebrain, in the field from asuperconducting magnet
www.rtr
i.or.jp/rd/maglev/html/en
glish/maglev_frame_E.html
www.lanl.gov/quarterly/q_spring03/meg_h
elmet.shtml
http://www.bestofjesse.com/projects
/indust/projec
t1.html
Bi min h m C nd n d M tt Ph i G p
5/26/2018 Basic Superconductivity
32/32
Ph i S mm S h l: S d ti it T d F
Birmingham Condensed Matter Physics Group
Thats all Folks!