Have a Problem You Can Solve That’s Not a Problem, It’s an OpportunityHave a Problem You Can’t Solve That is an Even Greater Opportunity

=========The Duckman

Prof. D.G. KuberkarDepartment of Physics

Saurashtra University

RAJKOT - 360 005, INDIA

E-mail: dgkuberkar@rediffmail.com

Historical Landmarks in Superconductivity

• 1911 Kamerlingh Onnes discovered superconductivity in Hg at Tc=4 K• 1913 Kamerlingh Onnes won the Nobel Prize in Physics• 1933 Meissner and Ochsenfeld discovered the Meissner Effect• 1941 Superconductivity in Nb nitride at Tc=16 K• 1953 Superconductivity reported in V3Si at Tc=17.5K• 1957 Microscopic BCS theory of superconductivity • 1962 The Josephson effect is predicted based on the BCS theory• 1962 Development of first superconducting wire (Westinghouse)• 1972 Bardeen, Cooper & Schrieffer win the Nobel Prize in Physics• 1973 Josephson wins the Nobel Prize in Physics• 1986 Müller and Bednorz (IBM-Zurich) discovered High Temperature Superconductivity in La-Ba-Cu-O at Tc=35K• 1987 Müller and Bednorz win the Nobel Prize in Physics• 1987 Superconductivity found in YBCO copper oxide at Tc=92K !!!• 1988 Tc is pushed to 120K in a ceramic containing Ca and Tl• 1993 Superconductivity in HgBa2Ca2Cu3O8 at Tc=133K

Physical PropertiesPhysical Properties

Critical Temperature Critical Magnetic field Meissner Effect Isotope effect

What is superconductor?Superconductors have two outstanding features:

1) Zero electrical resistivity. • This means that an electrical current in a

superconducting ring continues indefinitely until a force is applied to oppose the current.

2) The magnetic field inside a bulk sample is zero (the Meissner effect).

• When a magnetic field is applied current flows in the outer skin of the material leading to an induced magnetic field that exactly opposes the applied field.

• The material is strongly diamagnetic as a result. • In the Meissner effect experiment, a magnet

floats above the surface of the superconductor

WHAT IS SUPERCONDUCTIVITY ?

For some materials, the resistivity vanishes at some low temperature: they become superconducting.

Superconductivity is the ability of

certain materials to conduct

electrical current with no

resistance. Thus, superconductors

can carry large amounts of current

with little or no loss of energy.

Type I superconductors: pure metals, have low critical field

Type II superconductors: primarily of alloys or inter-metallic compounds.

The Critical Field

• An important characteristic of all superconductors is that the superconductivity is "quenched" when the material is exposed to a sufficiently high magnetic field.

• This magnetic field, Hc, is called the critical field. • Type II superconductors have two critical fields. • The first is a low-intensity field, Hc1, which partially

suppresses the superconductivity. • The second is a much higher critical field, Hc2, which

totally quenches the superconductivity.

The Critical Field

• The critical field, HC, that destroys the superconducting effect obeys a parabolic law of the form:

where Ho = constant, T = temperature, Tc = critical temperature.

• In general, the higher Tc, the higher Hc.

2

1C

OC

T

THH

Heat Capacity Isotope effect

massisotopicM

MTC

.

2/1

MEISSNER EFFECT

B

T > TC T < TC

B

When you place a superconductor in a magnetic field, the field is expelled below TC.

Magnet

Superconductor

Currents i appear, to cancel B.

i x B on the superconductorproduces repulsion.

Types I Superconductors

• There are 30 pure metals which exhibit zero resistivity at low temperature.

• They are called Type I superconductors (Soft Superconductors).

• The superconductivity exists only below their critical temperature and below a critical magnetic field strength.

Mat. Tc (K)

Be 0

Rh 0

W 0.015

Ir 0.1

Lu 0.1

Hf 0.1

Ru 0.5

Os 0.7

Mo 0.92

Zr 0.546

Cd 0.56

U 0.2

Ti 0.39

Zn 0.85

Ga 1.083

Mat. Tc (K)

Gd* 1.1

Al 1.2

Pa 1.4

Th 1.4

Re 1.4

Tl 2.39

In 3.408

Sn 3.722

Hg 4.153

Ta 4.47

V 5.38

La 6.00

Pb 7.193

Tc 7.77

Nb 9.46

Type I Superconductors

Type II Superconductors

• Starting in 1930 with lead-bismuth alloys, were found which exhibited superconductivity; they are called Type II superconductors (Hard Superconductors).

• They were found to have much higher critical fields and therefore could carry much higher current densities while remaining in the superconducting state.

Type II Superconductors

Compound TC (K)

   

PbMo6S8 12.6

SnSe2(Co(C5H5)2)0.33 6.1

K3C60 19.3

Cs3C6040 (15 kbar applied pressure)

Ba0.6K0.4BiO3 30

Lal.85Sr0.l5CuO4 40

Ndl.85Ce0.l5CuO4 22

YBa2Cu3O7 90

Tl2Ba2Ca2Cu3O10 125

HgBa2Ca2Cu3O8+d 133

Record TC versus Year Discovered

0

20

40

60

80

100

120

140

160

180

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

TC (

K)

Hg

NbNNb3Ge

La-Ba-Cu-O

La-Sr-Cu-O

YBa2Cu3O7

Bi2Sr2Ca2Cu3O8

Tl-Ba-Ca-Cu-O

HgBa2Ca2Cu2O8

HgBa2Ca2Cu2O8 Pressure

1986

BSC Theory

BSC Theory

[1] Critical temp of mercury with isotopic man 199.5 is 4.1850K. Calculate its critical temperature when its isotopic mass

changes to 203.4

[2] Calculate JC for 1 mm dia wire of bad at (a) 4.2 K and (b) 7KA parabolic dependence of HC upon T may be assumed. Given

TC for lead is 7.18 K and HC for lead is 6.5 × 104 amp/meter.

Magnetic Sensors Gradiometers Oscilloscopes Decoders Analogue to Digital Converters Samplers Oscillators Microwave Amplifiers Sensors for Biomedical Scientific and Defense Purposes Digital Circuit Development for Integrated Circuits Microprocessors Random Access Memories

APPLICATIONS: Medical

The superconducting magnet coils produce a large and uniform magnetic field inside the patient's body.

MRI (Magnetic Resonance Imaging) scans produce detailed images of soft tissues.

APPLICATIONS: Power

Superconducting Transmission CableFrom American Superconductor

The cable configuration features a conductor made from HTS wires wound around a flexible hollow core. Liquid nitrogen flows through the core, cooling the HTS wire to the zero resistance state.

The conductor is surrounded by conventional dielectric insulation. The efficiency of this design reduces losses.

High Magnetic Field

High Power

High Pressure

Set-up forHigh Pressure

Cooper Pairs

Breaking of Cooper Pairs

Due to Magnetic

Fields

APPLICATIONS: SuperconductingMagnetic Levitation

The track are walls with a continuous series of vertical coils of wire mounted inside. The wire in these coils is not a superconductor.

As the train passes each coil, the motion of the superconducting magnet on the train induces a current in these coils, making them electromagnets.

The electromagnets on the train and outside produce forces that levitate the train and keep it centered above the track. In addition, a wave of electric current sweeps down these outside coils and propels the train forward.

The Yamanashi MLX01MagLev Train