From UPSC perspective, the following things are important :
Prelims level : Superconductivity in Mercury
Mains level : Not Much
This newscard is an excerpt from the original article published in TH.
What is a superconductor?
- A superconductor is defined as a substance that offers no resistance to the electric current when it becomes colder than a critical temperature.
- Some of the popular examples of superconductors are aluminium, magnesium diboride, niobium, copper oxide, yttrium barium and iron pnictides.
How mercury becomes superconductor?
- In 1911, Dutch physicist Heike Kamerlingh Onnes discovered superconductivity in mercury.
- He found that at a very low temperature, called the threshold temperature, solid mercury offers no resistance to the flow of electric current.
How is mercury capable of achieving superconductivity?
Ans. Bardeen-Cooper-Schrieffer (BCS) theory
- Scientists classified mercury as a conventional superconductor because its superconductivity could be explained by the concepts of Bardeen-Cooper-Schrieffer (BCS) theory.
- While scientists have used the BCS theory to explain superconductivity in various materials, they have never fully understood how it operates in mercury — the oldest superconductor.
- The researchers used state-of-the-art theoretical and computational approaches and found that all physical properties relevant for conventional superconductivity are anomalous in some respect in mercury.
How BCS explains it?
- In BCS superconductors, vibrational energy released by the grid of atoms encourages electrons to pair up, forming so-called Cooper pairs.
- These Copper pairs can move like water in a stream, facing no resistance to their flow, below a threshold temperature.
- By including certain factors that physicists had previously side-lined, the group’s calculations led to a clearer picture of how superconductivity emerges in mercury.
- For example, when the researchers accounted for the relationship between an electron’s spin and momentum, they could explain why mercury has such a low threshold temperature (around –270°C).
Coulomb repulsion and Mercury
- Similarly, the group found that one electron in each pair in mercury occupied a higher energy level than the other.
- This detail reportedly lowered the Coulomb repulsion (like charges repel) between them and nurtured superconductivity.
- Thus, the group has explained how mercury becomes a superconductor below its threshold temperature.
- Their methods and findings suggest that we could have missed similar anomalous effects in other materials, leading to previously undiscovered ones that can be exploited for new and better real-world applications.
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