What is Superconductivity?

Superconductivity was discovered by Dutch Physicist Heike Kamerlingh Onnes in 1911 in Leiden. He was awarded the Nobel Prize in Physics in 1913 for his low-temperature research. Some materials when they are cooled, below certain temperature their resistivity get abolished means they exhibit the infinite conductivity.

The property / phenomenon of infinite conductivity in materials is called superconductivity.

The temperature at which the metals change from normal conducting state to superconducting state, is called critical temperature/transition temperature. An example of superconductors, is Mercury. It becomes superconductor at 4k. In superconducting state the materials expel the magnetic field. A transition curve for mercury is shown in figure below-

The transition from normal conducting state to superconducting state is reversible. Moreover, below critical temperature the superconductivity can be abolished either by passing sufficient large current through conductor itself or by applying sufficient strong external magnetic field. Below critical temperature/transition temperature, the value of current through conductor itself at which the superconducting state abolished is called critical current. As the temperature (below the critical temperature) reduces the value of critical current increase. The value of critical current increase with decrease in temperature. The value of critical magnetic field also depends on temperature. As the temperature (below the critical temperature) reduces the value of critical magnetic field increase.

Superconductor Metals

Some metals when they are cooled below their critical temperature exhibits the zero resistivity or infinite conductivity. These metal are called superconductor metals. Some metals showing superconductivity and their critical temperatures/transition temperature are listed in table below –

SL	Superconductor	Chemical Symbol	Critical/Transition Temperature TC(K)	Critical Magnetic Field BC(T)
1	Rhodium	Rh	0	0.0000049
2	Tungsten	W	0.015	0.00012
3	Beryllium	Be	0.026
4	Iridium	Ir	0.1	0.0016
5	Lutetium	Lu	0.1
6	Hafnium	Hf	0.1
7	Ruthenium	Ru	0.5	0.005
8	Osmium	Os	0.7	0.007
9	Molybdenum	Mo	0.92	0.0096
10	Zirconium	Zr	0.546	0.0141
11	Cadmium	Cd	0.56	0.0028
12	Uranium	U	0.2
13	Titanium	Ti	0.39	0.0056
14	Zinc	Zn	0.85	0.0054
15	Gallium	Ga	1.083	0.0058
16	Gadolinium	Gd	1.1
17	Aluminium	Al	1.2	0.010
18	Protactinium	Pa	1.4
19	Thorium	Th	1.4	0.013
20	Rhenium	Re	1.4	0.030
21	Thallium	Tl	2.39	0.018
22	Indium	In	3.408	0.028
23	Tin	Sn	3.722	0.030
24	Mercury	Hg	4.153	0.040
25	Tantalum	Ta	4.47	0.083
26	Vanadium	V	5.38	0.031
27	Lanthanum	La	6.0	0.11
28	Lead	Pb	7.193	0.080
29	Technetium	Tc	7.77	0.040
30	Niobium	Nb	9.46	0.820

Properties of Superconductors

The superconducting material shows some extraordinary properties. Some of these properties are listed below

Zero electric resistance (infinite conductivity)
Meissner Effect: Expulsion of magnetic field
Critical Temperature/transition temperature
Critical Magnetic field
Persistent currents
Josephson Currents
Critical current

Applications of Superconductivity

In modern field of technology the superconductivity is widely used in different fields of technology. Some of these applications are listed below-

Medical: MRI (Magnetic Resonance Imaging), Ultra-Low Field Magnetic Resonance Imaging (ULF-MRI), Magneto-encephalography (MEG) and Magnetic Source Imaging (MSI), Magneto-cardiography (MCG) etc.
Electric field: Generators, motors, transformers, relays, magnetic energy storages (SMES), superconducting magnets, HTS Induction Heater, Fusion etc.
Electronics: SQUIDS (superconducting quantum interference device), High Speed computing, Quantum computing, Sensors, filters, circuitry, radar etc.
Transportation: Magnetically levitated trains, Marine Propulsion (magneto-hydrodynamic), Marine Propulsion (motor) etc.
Physics: Particle Accelerators, Magnets, Plasma / fusion research etc.

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