PAUL SCHERRER INSTITUTPAUL SCHERRER INSTITUT

101 years of superconductivity

Kazimierz Conder

Laboratory for Developments and Methods, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland

kazimierz.conder@psi.ch

2

Temperature

Resi

stiv

ity Kelvin (1902)

Matthiessen (1864)

Dewar (1904)

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.

Hydrogen was liquefied (boiling point 20.28 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?

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.

From: Rudolf de Bruyn Ouboter, “Heike Kamerlingh Onnes’sDiscovery of Superconductivity”, Scientific American March 1997

Hg TC=4.2K

1895 William Ramsay in England discovered helium on the earth 1908 H. Kamerlingh Onnes liquefied helium (boiling point 4.22 K)

Superconductivity- discovery I

4

Superconductivity- discovery II

•Liquid Helium (4K) (1908). Boiling point 4.22K.

•Superconductivity in Hg TC=4.2K (1911)

„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)

5

Further discoveries

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=125K1993: Hg-Ba-Ca-Cu-O TC=133K

(A. Schilling, H. Ott, ETH Zürich)

1911-1986: “Low temperature superconductors” Highest TC=23K for Nb3Ge

6

1920 1940 1960 1980 20000

20

40

60

80

100

120

140

Cs2RbC

60

MgB2

LHe

Liquid nitrogen

HgBa2Ca

2Cu

3O

8

Tl2Sr

2Ca

2Cu

3O

10

Bi2Sr

2Ca

2Cu

3O

10

YBa2Cu

3O

7

La2-x

SrxCuO

4

Ba1-x

KxBiO

3

BaPb1-x

BixO

3

NaxWO

3NbO

Nb3Ge

Nb3SnNbN

NbPbHg

TC [

K]

Year

7

The current can flow 100 000 years!!

Zero resistivity

Low temperatures:LN2 -1960C (77K)

8

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.

Meissner-Ochsenfeld-effect

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

The lattice deformation creates a region of relative positive charge which can attract another electron.

An electron on the way through the lattice interacts with lattice sites (cations). The electron produces phonon.

1957 John Bardeen, Leon Cooper, and John Robert Schrieffer

During one phonon oscillation an electron can cover a distance of ~104Å. The second electron will be attracted without experiencing the repulsing electrostatic force .

John Bardeen, Leon Neil Cooper, John Robert Schrieffer

Nobel Prize in Physics 1972

"for their jointly developed theory of superconductivity, called the BCS-theory”

e-

e-

Phonon

Coherence length

Cooper pair model

12

Fermie und Bose-Statistic

•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.

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.

Energy

Density of states

Energy

Density of states

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).

e-

e-

Phonon

14

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.

BCS Theory: some consequences

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

15

What 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)

A current: produces magnetic field which in turn destroys superconductivity.

Current density

Temperature

Magnetic field

16

Coherence length

Coherence length is the distance between the carriers creating a Cooper-Pair.

GL

Superconductor

Concentration C-PISL SL

x< GL

Coherence length is the largest insulating distance which can be tunneled by Cooper-Pairs.

SC SC

(Xi)

"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".

Nobel Prize in Physics 1973

Brian David JosephsonJosephson discovered in 1963 tunnelling effect being 23-years old PhD student

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

ISL SL

x< GL

SC SC

18

Penetration depth

depicts the distance where B(x) is e-time smaller than on the surface

0

(T)=0*(1-(T/T

C)4)-0.5

TC

Ein

drin

gtie

fe

TemperaturTemperature

Pen

etra

tion

dept

h Superconductor

19

Ginzburg-Landau Parameter =/GL

Tc [nm] [nm]

Al 1.2 16 1600 0.01Sn 3.7 34 230 0.16Pb 7.2 37 83 0.4

<1/2=0.71 Superconductor Type I

Tc [nm] [nm]

Nb 9.3 39 38 1Nb3Sn 18 80 3 27YBa2Cu3O7 93 150 1.5 100Rb3C60 30 247 2.0 124Bi2Sr2Ca2Cu3O10 110 200 1.4 143

>0.71 Superconductor Type II

20

Superconductor type I (/GL<0.71) in a magnetic field

Bi=Ba+0

M

Superconductor Bi=0

Normal conductor Bi=Ba

Negative units !

The field inside the superconductor

The field created on the surface of the superconductor compensating the outside field

Outside field

Outside field BaOutside field Ba

Insi

de fi

eld

Bi

Mag

neti

zati

on

–μ

0M

21

Superconductor type II in a magnetic field

Vortex-lattice in superconductor type II. Magnetic flux of a vortex is quantized: 0=h/2e2.07·10-15Tm2

Bi=Ba+0M

Outside field Ba

Outside field Ba

Mag

neti

zati

on

–μ

0M

Avera

ge insi

de fi

eld

Bi

Meissner phase

Mixed phase

Normal condu-ctor

22

Superconductor type II. B-T-Diagram

Mixed phase

Meissner phase

Normal state

Temperature T

Mag

neti

c in

du

ctio

n B

STM (Scanning Tunneling Microscopy). Abrikosov-lattice in NbSe2

H. Hess, R.B. Robinson, and J.V. Waszczak, Physica B 169 (1991) 422

Alexei A. Abrikosov, Vitaly L. Ginzburg, Anthony J. Leggett

Nobel Prize in Physics 2003

"for pioneering contributions to the theory of superconductors and superfluids".

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Type IIType I

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Perovskite ABX3

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.

X

A

B

26

La, Sr

Cu

O

0.0 0.1 0.2 0.310

100

La2-x

SrxCuO

4

Insu

lato

r

Met

al

An

tife

rro

ma

gn

et

Superconductor

TN

TC

Tem

pera

ture

[K]

Sr-content x, (holes per CuO2-layer)

2SrO 2Sr‘La + 2Ox

O + VO

VO+ 0.5O2 Ox

O+ 2h

(LaBa)2 CuO4 TC=35K K.A. Müller und G. Bednorz (IBM Rüschlikon 1986 )

High Temperature Superconductor. La2-

xSrxCuO4

27

CuO2 –layer

5-fold Cu coordination

CuO-chain

4-fold Cu coordination

BaO

Y

Perovskite

“YBa2Cu3O9

”

High Temperature Superconductor: YBa2Cu3O7-x

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Oxygen doping in YBa2Cu3O7-x

6.0 6.2 6.4 6.6 6.8 7.00

20

40

60

80

100

Superconductor

YBa2Cu

3O

7-

Te

mp

era

ture

[K]

Oxygen content (7-)

TC

200 400 600 800 100098.5

99.0

99.5

100.0

YBa2Cu

3O

6.985

Oxy

gen

inde

x

Wei

ght

[%

]

Temperature [oC]

6.4

6.6

6.8

7.0

Thermogavimetry

Oxygen content depends on temperature and oxygen partial pressure

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Layered structure of YBa2Cu3O7-x

Conducting CuO2 layers

Charge reservoir

holes

electrons

holes

2Cu2+ + 0.5O2 2Cu3+ +O2-

2CuxCu + V

O +0.5O2 2CuCu +

OxO

2CuCu 2Cux

Cu + 2h

Y

BaO

CuO

CuO2

Conducting CuO2 layers

30

YBa2Cu3O7 TC=93

ab [Å] c [Å] ab [Å] c [Å]

1500 6000 15 4

8.3Å

3.4Å

Bi2Sr2Ca2 Cu3O10 TC=110

ab [Å] c [Å] ab [Å] c [Å]

2000 10 000 13 2

Cooper-pairs can not tunnel through the charge reservoir!

For YBa2Cu3O7 single crystals at 4.2Kjc(ab)~107A/cm2, jc(c)~105A/cm2

Un

it c

ell

Layered structure of YBa2Cu3O7-x. Anisotropy

31

C a

C a

C a

C a

C a

C a

Bi2Sr2Ca2Cu3O10 2223TC=110K

Bi2Sr2CaCu2O8

2212 TC=95KBi2Sr2CuO6 2201TC=20K

Bi-Sr-Ca-Cu-O

BiO

SrOCuO2 Ca

BiO

32

HgBa2Can-1CunO2n+2 “Hg-12(n-1)n”

1 2 3 4 5 6 7

90

100

110

120

130

140

Te

mp

era

ture

[K

]

Number of CuO2-layers in the unit cell

TC für 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

33

Sm TC=55K

April, 2008

Magnetic ion in the structure

Cs0.8(FeSe0.98)2

FeSe

CsIntercalation

K0.8(FeSe0.98)2

Cs0.8(FeSe0.98)2

Crystal growth in Cs (or K)- vapour in quartz ampoules at 1050oC

New superconductor Lix(C5H5N)yFe2-zSe2

arXiv:1206.7022

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

Synthesized via intercalation of dissolved alkaline metal (Li) in anhydrous pyridine at room temperature.

C5H5N

36

USOUS

OUnidentified Superconducting

Object

37American Superconductor

Extrusion

Abfüllen in Silberröhrchen und Schweissen

Extrusion

Walzen und Erhitzen bei800-900oC

c ab

Applications. Wires and bands.

38

Applications. Wires and bands.

Cross section of HTC

band

American Superconductor Corporation

HTC Cable

39

Application. Industry.

MagLev – train (magnetic levitation)

SMES: Superconducting Magnetic Energy StorageSaves energy in form of magnetic field produced by a superconducting coil.

Magnetic bearing

A flywheel in a vacuum chamber – energy accumulator.

Summary

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

A spin of a Cooper pair is:

1/21

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

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