How to tell if a material is a superconductor?

Context: In the last week of July, researchers in South Korea said they had discovered that a material called LK-99 is a room-temperature superconductor. Independent researchers will have to check whether LK-99 is really a room-temperature superconductor before it is accepted as a legitimate claim.

What are Superconductors?

Superconductors are materials that when cooled to temperatures ranging from near absolute zero (0 degrees Kelvin, -273 degrees Celsius) have zero resistance or do not resist the flow of current.

The temperature at which electrical resistance is zero is called the critical temperature (Tc)  and this temperature is a characteristic of the material. 

E.g., Aluminium, niobium, magnesium diboride, yttrium barium copper oxide etc.

However, every superconductor made so far has required extraordinarily high pressures (millions of Pascal), and very low temperatures. E.g., Aluminium becomes superconducting at temperatures less than (minus) –250° C. 

Hence, scientists have been looking for such materials for decades which can remain superconductors at room temperature. 

Important properties of Superconductors:

Electronic effect (Infinite conductivity with Zero resistance) – The material will transport an electric current with zero resistance. 

(When the temperature of superconductors is reduced below a critical temperature, its resistance suddenly reduces to zero and thus it offers infinite conductivity). E.g., Mercury becomes a superconductor below 4 kelvin.

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  • Magnetic effect (Complete expulsion of Magnetic field) – Superconductors are diamagnetic i.e., they oppose the magnetic field or do not allow the magnetic field lines to penetrate them. (This phenomenon is called Meissner effect)
    • However, there is a certain value of the magnetic field (critical magnetic field) beyond which the superconductors lose superconductivity and convert into conductors. 
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  • Elimination of the loss of energy: Superconductors can be used to make longer-lasting batteries and more-efficient power grids.
    • Need: Presently, a portion of the electricity generated at every power plant is lost during transmission because the wires and cables that carry the current have electrical resistance.
    • Significance of Superconductors: Once an electric current passes over a superconducting material, it can continue to flow without receiving power from any source as none of the energy involved is lost as heat.
  • Potential applications include– Magnetic-energy storage systems, magnetic levitation trains,  superconducting magnetic refrigerators, etc.

Huge potential for revolutionary technologies, including efficient quantum computers, as superconductors can exhibit quantum phenomena.

Source: The Hindu

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