- Superconductivity Definition: Superconductivity is defined as the property of certain materials to have zero electrical resistance at very low temperatures.
- Critical Temperature: The critical temperature is the specific temperature below which a material becomes superconducting.
- Meissner Effect: Superconductors exhibit the Meissner effect, where they expel magnetic fields when cooled below their critical temperature.
- Critical Current and Magnetic Field: Superconductivity is lost if the current through the material exceeds the critical current or if an external magnetic field exceeds the critical magnetic field.
- Applications of Superconductivity: Superconductivity is used in medical imaging, quantum computing, maglev trains, and particle accelerators.
Superconductivity was discovered by Dutch physicist Heike Kamerlingh Onnes in 1911 in Leiden. He won the Nobel Prize in Physics in 1913 for his low-temperature research. Some materials, when cooled below a certain temperature, lose all electrical resistance and exhibit infinite conductivity.
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 a normal conducting state to a superconducting state is reversible. Below the critical temperature, superconductivity can be destroyed by a large current or a strong external magnetic field. The current at which superconductivity is lost is called the critical current, and it increases as the temperature decreases. Similarly, the critical magnetic field also increases as the temperature drops.
Superconductor Metals
Some metals, when cooled below their critical temperature, exhibit zero resistivity or infinite conductivity. These metals are called superconductors metals. Here are some metals that show superconductivity and their critical temperatures:
| 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
Superconducting materials have extraordinary properties, including:
- 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
Superconductivity is widely used in various fields, including: –
- 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.
