Superconductivity of Mercury

In News

• Recently, a research group has discovered a clear picture of superconductivity in Mercury.

Key Points

• Discovery: 
  • In 1911, Dutch physicist Heike Kamerlingh Onnes discovered superconductivity in mercury. 
  • At a very low temperature, called the threshold temperature, solid mercury offers no resistance to the flow of electric current.
• The BCS theory:
  • Mercury was later classified as a conventional superconductor because its superconductivity could be explained by the concepts of this theory.
  • 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.
  • The theory has been used to explain superconductivity in various materials.
  • Although the clear picture of how it operates in mercury, the oldest superconductor, had been undiscovered. 

Latest Development

• Research Group: 
  • A group of researchers from Italy filled this gap as they wrote in their paper published in the journal,  Physical Review B.
• Reason in Mercury: 
  • 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.
• Threshold temperature: 
  • They were able to work out a theoretical description for superconductivity in mercury that predicted its threshold temperature to within 2.5% of the observed value.
• New and old factors taken into consideration: 
  • By including certain factors (like Cooper Pairs) that were earlier sidelined, 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:
  • It was 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.

Superconductor & Superconductivity

• Superconductor: 
  • A superconductor is a material that can conduct electricity or transport electrons from one atom to another with no resistance.
  • This happens at temperatures between 240 K and 275 K, that is, approximately between –33 degrees Celsius and 2 degrees Celsius.
  • This means no heat, sound or any other form of energy would be released from the material when it has reached the temperature at which the material becomes superconductive.
  • Superconductors are diamagnetic: 
    • A diamagnetic substance repels an external magnetic field, in sharp contrast to normal magnetism, or ferromagnetism, under which a substance is attracted by an external magnetic field.
• Disadvantage: 
  • Currently, an excessive amount of energy is used in the cooling process making superconductors inefficient and uneconomical.
• Superconductivity:
  • Superconductivity at temperatures below zero degree celcius makes its practical utility very difficult.
• Applications:
  • These are used in the memory component of computers, under sea communication and submarine detection.
  • Also, used in medical diagnostics, e.g., in magnetic imaging devices like Nuclear Magnetic Resonance (NMR).
  • Used for levitation in high speed trains.
  • SQUIDS (Superconducting Quantum Interference Devices) can be used to take magnetic cardiograms based on magnetic fields generated by electric currents in the heart.

Way Ahead

• This opens avenues to check other materials for superconductivity which shows similar anomalous effects in other materials.
• It can be exploited for new and better real-world applications.

Source:  TH