It is extremely rare to find natural materials which display superconductivity. While some elements exist in metallic form, superconductivity has only been found in meteorites that contain lead, tin, and indium alloys. Superconducting compounds are even more scarce, with only the mineral covellite showing superconductivity in naturally occurring samples.
(Photo: Wikimedia Commons/ Edosz2010)
Search for Unconventional Superconductors
Superconductivity refers to the ability exhibited by a material to conduct electricity without losing energy. Superconductors have found applications in various fields, such as quantum computers, power cables, and medical MRI machines.
With our current technology, conventional superconductors are well understood but have low critical temperatures. A material's critical temperature is the highest temperature at which it acts as a superconductor.
It was in the 1980s when experts discovered unconventional superconductors, many of which possess much higher critical temperatures. Scientists used to believe that all these materials were grown in the laboratory, leading to the general belief that unconventional superconductivity is not a natural phenomenon. Finding superconductors in nature is difficult because most superconducting elements and compounds are metals that tend to react with other elements, such as oxygen.
Unveiling the Properties of Miassite Mineral
At Ames National Laboratory, scientists have identified the world's first unconventional superconductor with a chemical composition found in nature. Their findings, discussed in the study "Nodal superconductivity in miassite Rh17S15," provide more insight into a type of superconductivity that could lead to more sustainable and economical superconductor-based technology in the future.
According to Ruslan Prozorov, miassite is an interesting mineral for various reasons, one of which is its complex chemical structure. Miassite is one of the only four minerals found in nature that act as a superconducting compound when grown in the laboratory. Although this mineral was discovered near the Miass River in Chelyabinsk Oblast in Russia, it is rare and does not generally grow as well-formed crystals.
The research team used three methods to determine the nature of miassite's superconductivity. The main test, called the "London penetration depth", determined how far a weak magnetic field can penetrate the superconductor bulk from the surface of a material. In a conventional superconductor, this length is usually constant at low temperatures. Meanwhile, it varies linearly with the temperature when observed in unconventional superconductors. This test, therefore, confirms that miassite behaves as an unconventional superconductor.
In another test, the researchers introduced the defects in the miassite mineral. This involves bombarding the ions with high-energy electrons to knock them out of their positions. It creates defects in the crystal structure, causing changes in the material's critical temperature.
Since conventional superconductors are not sensitive to non-magnetic disorders, this test would show little or no change in a material's critical temperature. Unconventional superconductors, on the other hand, are highly sensitive to disorder, so the introduction of defects changes or suppresses the critical temperature. Moreover, it affects the critical magnetic field of the material.
The researchers discovered that both the critical temperature and the critical magnetic field in miassite behaved as predicted in unconventional superconductors. This investigation reveals that miassite is an unconventional superconductor with properties resembling high-temperature superconductors.
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