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Mercury Superconductivity

  • This news card is an excerpt from the original TH article.
  • A superconductor is a substance that offers no resistance to electric current when it cools below a critical temperature.
  • Aluminum, magnesium diboride, niobium, copper oxide, yttrium barium, and iron pnictides are some well-known superconductors.

What causes mercury to become a superconductor?

  • Heike Kamerlingh Onnes, a Dutch physicist, discovered superconductivity in mercury in 1911.
  • He discovered that solid mercury offers no resistance to the flow of electric current at a very low temperature, known as the threshold temperature.

What makes mercury capable of superconductivity?

  • The Bardeen-Cooper-Schrieffer (BCS) theory provides an answer.
  • Mercury was classified as a conventional superconductor by scientists because its superconductivity could be explained by Bardeen-Cooper-Schrieffer (BCS) theory concepts.
  • While the BCS theory has been used to explain superconductivity in a variety of materials, scientists have never fully understood how it works in mercury, the oldest superconductor.
  • The researchers used cutting-edge theoretical and computational approaches to discover that all physical properties relevant to conventional superconductivity in mercury are anomalous in some way.

How does BCS explain it?

  • The vibrational energy released by the grid of atoms in BCS superconductors encourages electrons to pair up, forming so-called Cooper pairs.
  • Below a certain temperature, these copper pairs can move like water in a stream, with no resistance to their flow.
  • The group’s calculations provided a clearer picture of how superconductivity emerges in mercury by including previously overlooked factors.
  • For example, by accounting for the relationship between an electron’s spin and momentum, the researchers were able to explain why mercury has such a low threshold temperature (around -270°C).

Coulomb repulsion and Mercury

  • Similarly, the researchers discovered that one electron in each pair of mercury electrons occupied a higher energy level than the other.
  • This detail is said to have reduced the Coulomb repulsion (like charges repel) between them, fostering superconductivity.
  • As a result, the researchers have explained how mercury becomes a superconductor below its critical temperature.
  • Their methods and findings imply that we may have overlooked similar anomalous effects in other materials, resulting in previously unknown ones that can be exploited for new and improved real-world applications.
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