1
Heike Kamerlingh Onnes’s
Discovery of Superconductivity
The turn-of-the-century race to reach temperatures
approaching absolute zero led to the unexpected discovery
of electric currents that flowed with no resistance
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Superconductivity, Exercises of Advanced Physics
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1
Heike Kamerlingh Onnes’s
Discovery of Superconductivity
The turn-of-the-century race to reach temperatures
approaching absolute zero led to the unexpected discovery
of electric currents that flowed with no resistance
2
Temperature
Resistivity
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
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 19
th
and beginning of the 20
th
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’s
Discovery of Superconductivity” , Scientific American March 1997
Hg T
C
=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
5
Superconductivity-
discovery II
Liquid Helium (4K)
(1908). Boiling
point 4.22K.
Superconductivity
in Hg T
C
=4.2K
„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
Resistivity R=0 below T
C
;
(R<
cm, 10
18
times
smaller than for Cu)
7
Further discoveries
1986 (January): High
Temperature Superconductivity
(LaBa)
2
CuO
4
T
C
=35K
K.A. Müller und G. Bednorz (IBM
Rüschlikon) (Nobel preis 1987)
1987 (January): YBa
2
Cu
3
O
7-x
T
C
=93K
1987 (December): Bi-Sr-Ca-Cu-O
T
C
=110K,
1988 (January): Tl-Ba-Ca-Cu-O T
C
=125K
1993: Hg-Ba-Ca-Cu-O T
C
=133K
(A. Schilling, H. Ott, ETH Zürich)
1911-1986: “Low temperature
superconductors” Highest T
C
=23K
for Nb
3
Ge
8
0
20
40
60
80
100
120
140
Cs
2
RbC
60
MgB
2
L
He
Liquid nitrogen
HgBa
2
Ca
2
Cu
3
O
8
Tl
2
Sr
2
Ca
2
Cu
3
O
10
Bi
2
Sr
2
Ca
2
Cu
3
O
10
YBa
2
Cu
3
O
7
La
2-x
Sr
x
CuO
4
Ba
1-x
K
x
BiO
3
BaPb
1-x
Bi
x
O
3
Na
x
WO
3
NbO
Nb
3
Ge
Nb
3
Sn
NbN
Nb
Pb
Hg
T
C
[K]
Year
Effect of Magnetic Field
Critical magnetic field (H
C
Minimum magnetic field
required to destroy the
superconducting property at
any temperature
H
0
- Critical field at 0K
T - Temperature below T
C
T
C
- Transition Temperature
Superconducting
Normal
T (K) T
C
H
0
H
C
Element H
C
at 0K
(mT)
Nb 198
Pb 80.
Sn 30.
2
0
1
C
C
T
H H
T
MEISSNER EFFECT
When the superconducting material is placed in a magnetic field
under the condition when T≤T
C
and H ≤ H
C
, the flux lines are
excluded from the material.
Material exhibits perfect diamagnetism or flux exclusion.
Deciding property
χ = I/H = -
Reversible (flux lines penetrate when T ↑ from T
C
Conditions for a material to be a superconductor
i. Resistivity ρ = 0
ii. Magnetic Induction B = 0 when in an uniform magnetic field
Simultaneous existence of conditions
13
A superconductor is a perfect
diamagnet. Superconducting
material expels magnetic flux
from the interior.
W. Meissner, R. Ochsenfeld
On the surface of a
superconductor (T<T
C
superconducting current will be
induced. This creates a magnetic
field compensating the outside
one.
Meissner-Ochsenfeld-effect
Screening (shielding ) currents
Magnetic
14
Superconducting elements
Ferromagnetic elements are not superconducting
The best conductors (Ag, Cu, Au..) are not superconducting
Nb has the highest T
C
= 9.2K from all the elements
John Bardeen, Leon Neil Cooper, John Robert Schrieffer
Nobel Prize in Physics
"for their jointly developed
theory of superconductivity,
called the BCS-theory”
e
-
e
-
Phonon
Coherence
length
Cooper pair model
17
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
Types of Superconductors
Type I
Sudden loss of magnetisation
Exhibit Meissner Effect
One H
C
= 0.1 tesla
No mixed state
Soft superconductor
Eg.s – Pb, Sn, Hg
Type II
Gradual loss of magnetisation
Does not exhibit complete
Meissner Effect
- Two H
C
s – H
C
& H
C
(≈30 tesla)
Mixed state present
Hard superconductor
Eg.s – Nb-Sn, Nb-Ti
M
H
H
C
Superconducting
Normal
Superconducting
-M
Normal
Mixed
H
C
H
C
H
C
H