101 years of superconductivity

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101 years of superconductivity Kazimierz Conder

Laboratory for Developments and Methods, Paul
Scherrer Institute, 5232 Villigen PSI, Switzerland
kazimierz.conder_at_psi.ch
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Electrical resistivity at low temperatures
Kelvin Electrons will be frozen resistivity
grows till ?. Dewar the lattice will be frozen
the electrons will not be scattered.
Resistivity wiil decrese till 0. Matthiesen
Residual resistivity because of contamination and
lattice defects.
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Superconductivity- discovery I
1895 William Ramsay in England discovered helium
on the earth 1908 H. Kamerlingh Onnes liquefied
helium (boiling point 4.22 K)
Resistivity at low temperatures- pure mercury
(could repeatedly distilled producing very pure
samples).

• Repeated resistivity measurements indicated zero
  resistance at the liquid-helium temperatures.
  Short circuit was assumed!
• During one repetitive experimental run, a young
  technician fall asleep. The helium pressure (kept
  below atmospheric one) slowly rose and,
  therefore, the boiling temperature. As it passed
  above 4.2 K, suddenly resistance appeared.

Hg TC4.2K
From Rudolf de Bruyn Ouboter, Heike Kamerlingh
Onness Discovery of Superconductivity,
Scientific American March 1997
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Superconductivity- discovery II

• Liquid Helium (4K) (1908). Boiling point 4.22K.
• Superconductivity in Hg TC4.2K (1911)

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Further discoveries
1911-1986 Low temperature superconductors
Highest TC23K for Nb3Ge
1986 (January) High Temperature
Superconductivity (LaBa)2 CuO4 TC35K K.A. Müller
und G. Bednorz (IBM Rüschlikon) (Nobel preis 1987)
1987 (January) YBa2Cu3O7-x TC93K
1987 (December) Bi-Sr-Ca-Cu-O TC110K, 1988
(January) Tl-Ba-Ca-Cu-O TC125K
1993 Hg-Ba-Ca-Cu-O TC133K (A. Schilling, H.
Ott, ETH Zürich)
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Zero resistivity
Low temperatures LN2 -1960C (77K)
The current can flow 100 000 years!!
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Meissner-Ochsenfeld-effect
A superconductor is a perfect diamagnet.
Superconducting material expels magnetic flux
from the interior. W. Meissner, R. Ochsenfeld
(1933)
On the surface of a superconductor (TltTC)
superconducting current will be induced. This
creates a magnetic field compensating the outside
one.
Screening (shielding ) currents
Magnetic levitation
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Superconducting elements

• Ferromagnetic elements are not superconducting
• The best conductors (Ag, Cu, Au..) are not
  superconducting
• Nb has the highest TC 9.2K from all the elements

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Classical model of superconductivity
1957 John Bardeen, Leon Cooper, and John Robert
Schrieffer
An electron on the way through the lattice
interacts with lattice sites (cations). The
electron produces phonon.
The lattice deformation creates a region of
relative positive charge which can attract
another electron.
During one phonon oscillation an electron can
cover a distance of 104Å. The second electron
will be attracted without experiencing the
repulsing electrostatic force .
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Nobel Prize in Physics 1972 "for their jointly
developed theory of superconductivity, called the
BCS-theory
John Bardeen, Leon Neil Cooper, John Robert
Schrieffer
Coherence length ?
Cooper pair model
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Fermie und Bose-Statistic
Cooper-Pairs are created with electrons with
opposite spins.

• Fermions- elemental particles with 1/2 spin
  (e.g. electrons, protons, neutrons..)
• Pauli-Principle every energy level can be
  occupied with maximum two electrons with opposite
  spins.

• Total spin of C-P is zero. C-P are bosons.
  Pauli-Principle doesnt obey.
• All C-P can have the same quantum state with the
  same energy.

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A movement of the C-P when a supercurrent is
flowing, is considered as a movement of a centre
of the mass of two electrons creating C-P.
Creation of a C-Pairs diminishes energy of
electrons. Breaking a pair (e.g. through
interaction with impurity site) means increase of
the energy.
All the C-P are in the same quantum state with
the same energy. A scattering by a lattice
imperfection (impurity) can not change quantum
state of all C-P at the same time (collektive
behaviour).
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BCS Theory some consequences
Good electrical conductors are showing no
superconductivity In case of good conductors is
the interaction of carriers with the lattice very
week. This is, however, important for
superconductivity.
Isotope effect The Cooper-Pairs are created
(glued) by the electron-phonon interaction.
Energy of the phonons (lattice vibrations)
depends on the mass of the lattice site .
Superconductivity (Tc) should depend on the mass
of the ions (atoms) creating the lattice.
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What destroys superconductivity?
A current produces magnetic field which in turn
destroys superconductivity.
High temperatures strong thermal vibration of
the lattice predominate over the electron-phonon
coupling.
Magnetic field the spins of the C-P will be
directed parallel. (should be antiparallel in
C-P)
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Coherence length ?
(Xi)
Concentration C-P
Superconductor
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Nobel Prize in Physics 1973
"for his theoretical predictions of the
properties of a supercurrent through a tunnel
barrier, in particular those phenomena which are
generally known as the Josephson effects".
Josephson discovered in 1963 tunnelling effect
being 23-years old PhD student
Brian David Josephson
The superconducting tunnel Josephson) junction
(superconductorinsulatorsuperconductor tunnel
junction (SIS) is an electronic device
consisting of two superconductors separated by a
very thin layer of insulating material
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Penetration depth
Superconductor
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Ginzburg-Landau Parameter ??/?GL
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Superconductor type I (?/?GLlt0.71) in a magnetic
field
The field created on the surface of the
superconductor compensating the outside field
BiBa?0M
The field inside the superconductor
Outside field
Negative units !
Magnetization µ0M
Inside field Bi
Outside field Ba
Outside field Ba
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Superconductor type II in a magnetic field
BiBa?0M
Normal condu-ctor
Meissner phase
Mixed phase
Magnetization µ0M
Average inside field Bi
Outside field Ba
Outside field Ba
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Superconductor type II. B-T-Diagram
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Nobel Prize in Physics 2003 "for pioneering
contributions to the theory of superconductors
and superfluids".
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Type II
Type I
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Perovskite ABX3
X
B
A
XO2-, F-, Cl-) Aalkali, alkali-earth and
rare-earth metals, Btransition metals (also Si,
Al, Ge, Ga, Bi, Pb)
Perovskite is named for a Russian mineralogist,
Count Lev Aleksevich von Perovski. The mineral
(CaTiO3) was discovered and named by Gustav Rose
in 1839 from samples found in the Ural Mountains.
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High Temperature Superconductor. La2-xSrxCuO4
(LaBa)2 CuO4 TC35K K.A. Müller und G. Bednorz
(IBM Rüschlikon 1986 )
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High Temperature Superconductor YBa2Cu3O7-x
BaO
Y
CuO2 layer 5-fold Cu coordination
CuO-chain 4-fold Cu coordination
Perovskite
YBa2Cu3O9
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Oxygen doping in YBa2Cu3O7-x
TC
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Layered structure of YBa2Cu3O7-x
CuO
BaO
CuO2
Y
Conducting CuO2 layers
holes
Charge reservoir
electrons
Conducting CuO2 layers
holes
2Cu2 0.5O2 ? 2Cu3 O2- 2CuxCu V? ?O
0.5O2 ? 2Cu?Cu OxO 2Cu?Cu ? 2CuxCu 2h?
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Layered structure of YBa2Cu3O7-x. Anisotropy
Cooper-pairs can not tunnel through the charge
reservoir!
3.4Å
YBa2Cu3O7 TC93 ?ab Å ?c Å ?ab Å ?c
Å 1500 6000 15 4
Unit cell
8.3Å
Bi2Sr2Ca2 Cu3O10 TC110 ?ab Å ?c Å ?ab
Å ?c Å 2000 10 000 13 2
For YBa2Cu3O7 single crystals at
4.2K jc(ab)107A/cm2, jc(c)105A/cm2
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Bi-Sr-Ca-Cu-O
BiO
BiO
SrO
CuO2
Ca
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HgBa2Can-1CunO2n2 Hg-12(n-1)n
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Magnetic ion in the structure
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Cs0.8(FeSe0.98)2
FeSe
Intercalation
Cs
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New superconductor Lix(C5H5N)yFe2-zSe2
Synthesized via intercalation of dissolved
alkaline metal (Li) in anhydrous pyridine at room
temperature.
C5H5N
Synthesis of a new alkali metal-organic solvent
intercalated iron selenide superconductor with
Tc45K A. Krzton-Maziopa, E. V. Pomjakushina, V.
Yu. Pomjakushin, F. von Rohr, A. Schilling, K.
Conder
arXiv1206.7022
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USO
USO
Unidentified Superconducting Object
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Applications. Wires and bands.
American Superconductor
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Applications. Wires and bands.
Cross section of HTC band American
Superconductor Corporation
HTC Cable
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Application. Industry.
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Summary

• History of discovery and farther development
• How it works (still open problem for HTc)
• What are the materials
• Potential applications

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A spin of a Cooper pair is
1/2 1
2 0
Most of the HTc superconductors are
Cuprates Nickelates
Cobaltates Manganates
Superconductors type II in comparison to type I
have shorter coherence length and longer penetration depth have shorter coherence length and shorter penetration depth
are cuprates (all other superconductors are type I) have longer coherence length and shorter penetration depth
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In the BCS theory it is assumed that the
interaction between electrons in Cooper pairs is
mediated by
photons Coulomb force
phonons magnetic interaction
Vortex phase is observed
For all superconductors type I Only in cuprates
For all superconductors above Tc For all superconductors type II
Isotope effect (Tc dependence on lattice mass) is
a proof of BCS theory (electron-phonon interaction) a proof that superconductor is of type II
only observed for hole doped superconductors not observed in superconductors
In case of many High Temperature superconductors
in order to achieve temperatures below Tc one can
use
Icewater Liquid nitrogen
Dry ice (solid CO2-sublimation at -78.5 C) No cooling is necessary