1. 101 years of superconductivity
                 
101 years of superconductivity
Kazimierz Conder
Laboratory for Developments and Methods, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland 1

2. Electrical resistivity at low temperatures
Kelvin (1902)
Matthiessen (1864)
Dewar (1904)
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.
Hydrogen was liquefied (boiling point K) for the first time by James Dewar in 1898
One of the scientific challenge at the end of 19th and beginning of the 20th century: How to reach temperatures close to 0 K?

3. 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 TC=4.2K
From: Rudolf de Bruyn Ouboter, “Heike Kamerlingh Onnes’s
Discovery of Superconductivity”, Scientific American March 1997

4. Superconductivity- discovery II
„Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconducting state“
H. Kamerlingh Onnes 1913 (Nobel preis 1913)
Resistivity R=0 below TC; (R<10-23 cm, 1018 times smaller than for Cu)
Liquid Helium (4K) (1908). Boiling point 4.22K.
Superconductivity in Hg TC=4.2K (1911) 4

5. Further discoveries
: “Low temperature superconductors” Highest TC=23K
for Nb3Ge
1986 (January): High Temperature Superconductivity (LaBa)2 CuO4 TC=35K
K.A. Müller und G. Bednorz (IBM Rüschlikon) (Nobel preis 1987)
1987 (January): YBa2Cu3O7-x TC=93K
1987 (December): Bi-Sr-Ca-Cu-O TC=110K,
1988 (January): Tl-Ba-Ca-Cu-O TC=125K
1993: Hg-Ba-Ca-Cu-O TC=133K
(A. Schilling, H. Ott, ETH Zürich)

7. The current can flow 100 000 years!!
Zero resistivity
Low temperatures:
LN C (77K)
The current can flow years!!

8. 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 (T<TC) superconducting current will be induced. This creates a magnetic field compensating the outside one.
Screening (shielding ) currents
Magnetic levitation

9. 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

10. 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 . 10 10

11. Nobel Prize in Physics 1972
"for their jointly developed theory of superconductivity, called the BCS-theory”
John Bardeen, Leon Neil Cooper, John Robert Schrieffer e-
Phonon
Coherence
length 
Cooper pair model

12. Fermie und Bose-Statistic
Energy
Density of states
Energy
Density of states
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 doesn’t obey.
All C-P can have the same quantum state with the same energy.

13. Creation of a C-Pairs diminishes energy of electrons
Creation of a C-Pairs diminishes energy of electrons. Breaking a pair (e.g. through interaction with impurity site) means increase of the energy.
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. e-
Phonon
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).

14. For most of the low-temperature superconductors =0.5
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.
TC~M-
For most of the low-temperature superconductors =0.5 14

15. What destroys superconductivity?
A current: produces magnetic field which in turn destroys superconductivity.
Current density
Temperature
Magnetic field
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)

16. Coherence length  (Xi) GL Concentration C-P SC SuperconductorSL
x< GL
Coherence length is the largest insulating distance which can be tunneled by Cooper-Pairs. SC
Concentration C-P
Superconductor Xi
GL
Coherence length is the distance between the carriers creating a Cooper-Pair.

17. 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 tunnelling effect being 23-years old PhD student
Brian David Josephson
The superconducting tunnel Josephson) junction (superconductor–insulator–superconductor tunnel junction (SIS) — is an electronic device consisting of two superconductors separated by a very thin layer of insulating material I SL
x< GL SC

18. Penetration depth Superconductor Penetration depth  Temperature
 depicts the distance where B(x) is e-time smaller than on the surface
Superconductor
Temperature
Penetration depth  18 18

19. Ginzburg-Landau Parameter =/GL
Tc  [nm] [nm]  Al Sn Pb
<1/2=0.71 Superconductor Type I
Tc  [nm] [nm]  Nb
Nb3Sn
YBa2Cu3O
Rb3C
Bi2Sr2Ca2Cu3O
>0.71 Superconductor Type II
Kappa

20. Superconductor type I (/GL<0.71) in a magnetic field
The field created on the surface of the superconductor compensating the outside field
The field inside the superconductor
Bi=Ba+0M
Outside field
Negative units !
Magnetization –μ0M
Inside field Bi
Outside field Ba
Outside field Ba
Das Feld im Inneren des Supraleiters
Das Feld, welches im Supraleiter aufgebaut wird, um das äussere Feld zu kompensieren
Superconductor Bi=0
Normal conductor Bi=Ba

21. Superconductor type II in a magnetic field
Bi=Ba+0M
Meissner phase
Mixed phase
Normal condu-ctor
Magnetization –μ0M
Average inside field Bi
Outside field Ba
Outside field Ba
Vortex-lattice in superconductor type II. Magnetic flux of a vortex is quantized:
0=h/2e2.07·10-15Tm2

22. Superconductor type II. B-T-Diagram
Mixed phase
Meissner
phase
Normal state
Temperature T
Magnetic induction B
STM (Scanning Tunneling Microscopy). Abrikosov-lattice in NbSe2
H. Hess, R.B. Robinson, and J.V. Waszczak, Physica B 169 (1991) 422 22

23. Alexei A. Abrikosov, Vitaly L. Ginzburg, Anthony J. Leggett
Nobel Prize in Physics 2003
"for pioneering contributions to the theory of superconductors and superfluids".

24. Type I
Type II

25. Perovskite ABX3 X B A X=O2-, F-, Cl-)
A=alkali, alkali-earth and rare-earth metals,
B=transition 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.

26. High Temperature Superconductor. La2-xSrxCuO4
(LaBa)2 CuO4 TC=35K K.A. Müller und G. Bednorz (IBM Rüschlikon 1986 )
La, Sr Cu O
2SrO  2Sr‘La + 2OxO + VO
VO+ 0.5O2 OxO+ 2h 26

27. High Temperature Superconductor: YBa2Cu3O7-x
BaO Y
CuO2 –layer
5-fold Cu coordination
CuO-chain
4-fold Cu coordination
Perovskite
“YBa2Cu3O9”

28. Oxygen doping in YBa2Cu3O7-xTC
Oxygen content depends on temperature and oxygen partial pressure

29. Layered structure of YBa2Cu3O7-x
BaO
CuO2 Y
Conducting CuO2 layers
holes
Charge reservoir
electrons
Conducting CuO2 layers
holes
2Cu O2  2Cu3+ +O2-
2CuxCu + V O +0.5O2  2CuCu + OxO
2CuCu  2CuxCu + 2h

30. Layered structure of YBa2Cu3O7-x. Anisotropy
Cooper-pairs can not tunnel through the charge reservoir!
3.4Å
YBa2Cu3O7 TC=93
ab [Å] c [Å] ab [Å] c [Å]
Unit cell
8.3Å
Bi2Sr2Ca2 Cu3O10 TC=110
ab [Å] c [Å] ab [Å] c [Å]
For YBa2Cu3O7 single crystals at 4.2K
jc(ab)~107A/cm2, jc(c)~105A/cm2

31. Bi-Sr-Ca-Cu-O BiO BiO SrO CuO2 Ca Bi2Sr2CuO6 2201 Bi2Sr2Ca2Cu3O10 2223
TC=110K
Bi2Sr2CaCu2O TC=95K
Bi2Sr2CuO
TC=20K
BiO
BiO
SrO
CuO2 Ca

32. HgBa2Can-1CunO2n+2 “Hg-12(n-1)n”
CuO2-layers
World record 133K !!!
ETH Zürich - A.Schilling, M.Cantoni, J.D. Guo, H.R.Ott, Nature, 362(1993)226
TC für HgBa2Can-1CunO2n+2
Hg-12(n-1)n

33. Magnetic ion in the structureSm
TC=55K
April, 2008

34. Cs0.8(FeSe0.98)2 FeSe Intercalation Cs
K0.8(FeSe0.98)2
Cs0.8(FeSe0.98)2
Crystal growth in Cs (or K)- vapour in quartz ampoules at 1050oC 34

35. 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 Tc≈45K
A. Krzton-Maziopa, E. V. Pomjakushina, V. Yu. Pomjakushin, F. von Rohr, A. Schilling, K. Conder
arXiv:

36. USO
USO
Unidentified Superconducting Object 36 36

37. Applications. Wires and bands.
Abfüllen in Silberröhrchen und Schweissen
Extrusion c ab
Extrusion
Walzen und Erhitzen bei oC
American Superconductor

38. Applications. Wires and bands.
Cross section of HTC band
American Superconductor Corporation
HTC Cable

39. Application. Industry. Magnetic bearing
A flywheel in a vacuum chamber – energy accumulator.
MagLev – train (magnetic levitation)
SMES: Superconducting Magnetic Energy Storage
Saves energy in form of magnetic field produced by a superconducting coil.

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

41. A spin of a Cooper pair is:
1/2 1 2
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

42. 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:
Ice+water
Liquid nitrogen
Dry ice (solid CO2-sublimation at −78.5 C)
No cooling is necessary