SUPERCONDUCTIVITY OF MERCURY

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Context

• Recently, Researchers from the University of L' Aquila Italy have found a comprehensive microscopic understanding of the super productivity of Mercury.

Mercury

• Mercury is a heavy, silvery-white metal that is liquid at room temperature.
• Compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity.
• It has a freezing point of −38.83 °C and a boiling point of 356.73 °C, both the lowest of any stable metal.
• It is found either as a native metal(rare) or in cinnabar, metacinnabar, sphalerite, corderoite, livingstonite, and other minerals, with cinnabar (HgS) being the most common ore.

Superconductivity

• Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material.
• In this, materials to conduct direct current (DC) electricity without energy loss when they are cooled below a critical temperature(referred to as T_c). These materials also expel magnetic fields as they transition to the superconducting state.
• This capacity produces interesting and potentially useful effects. Superconductivity was first observed in 1911 by H. K. Onnes, a Dutch physicist. 
• Superconductors have been employed in, or proposed for use in, an enormous variety of applications. Examples include high-speed magnetic-levitation trains, magnetic-resonance-imaging (MRI) equipment, ultra-high-speed computer chips, high-capacity digital memory chips, alternative energy storage systems, radio-frequency (RF) filters, radio-frequency amplifiers, sensitive visible-light and infrared detectors, miniaturized wireless transmitting antennas, systems to detect submarines and underwater mines, and gyroscopes for earth-orbiting satellites.

Superconductivity of Mercury

• 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.

The BCS theory

• Scientists later classified mercury as a conventional superconductor because its superconductivity could be explained by the concepts of Bardeen-Cooper-Schrieffer (BCS) theory.

BCS Theory BCS Theory describes superconductivity as a microscopic effect caused by a condensation of Cooper pairs- a pair of electrons in a superconductor that is attractively bound and has equal and opposite momentum and spin. Below a specific critical temperature, the electrons in a metal pair up to create bosons called Cooper pairs. These Copper pairs can move like water in a stream, facing no resistance to their flow, below a threshold temperature.

• 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.
• Now, recently, scientists have drawn a clear picture of how mercury becomes a superconductor.

Recent Research on Mechanism of Superconductivity in Mercury

• 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).
• The group found that one electron in each pair in mercury occupied a higher energy level than the other. This 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.

Closing Thought

• The 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.

https://www.thehindu.com/sci-tech/science/a-clear-picture-of-how-mercury-becomes-a-superconductor/article66346400.ece