On July 21, a group of physicists in South Korea reported that they had synthesised a material that was a superconductor at room temperature and ambient pressure. Scientists have been looking for such a material for decades now — a substance that can carry an electric current with zero losses. A not insignificant amount of electric current is lost today during transmission between a power plant and the point of consumption. A room-temperature superconductor would also bring considerable gains for heavy industrial and research applications, including medical diagnostics, mass spectrometers, nuclear reactor designs, and particle colliders. But has the South Korean group really found such a thing?
Superconductivity research is more than a century old and has developed in tandem with technologies to cool materials to very low temperatures and/or apply very high pressures and techniques to understand whether a material has really become superconducting at the microscopic scale. Both are highly sophisticated enterprises with very small margins of error.
Chart 1 | The chart shows the materials ordered by their critical temperature (Tc), the temperature below which they become superconducting (in kelvin)
Tc values vary depending on the material’s properties. Values here are indicative.
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The jump between magnesium diboride and YBCO, and up to HBCCO, is the result of a revolution in the late 1980s when physicists discovered the higher-temperature copper-oxide superconductors. The value of Tc makes the difference between cooling the material with liquid helium, which is relatively more difficult, and with liquid nitrogen. Copper-oxides can be cooled with liquid nitrogen to their Tc values. While this chart also shows LaH10 to be a room-temperature superconductor, there is a catch: it is one of a few materials that scientists found to become superconducting at or near room temperature but under enormous pressure (Chart 2).
Chart 2 | The chart shows the pressure required to induce a superconducting state in some materials. (Yellow) shows the critical pressure and (blue) shows the critical temperature.
In the past, more than a few claims of having discovered a room-temperature superconductor have been retracted after independent scrutiny has revealed some flaw. These are after all lucrative materials attached to significant scientific credibility and honour, so scientists are wary of being ‘scooped’.
*Independent experts have raised some concerns with the data.
Chart 3 | The chart shows when superconductivity was discovered in each material, grouped by type. This list is not exhaustive
BCS=Bardeen-Cooper-Schrieffer; HF= Heavy fermion; Sr=-based= Strontium-based
The field has been rocked by controversies. One was when the German physicist Jan Hendrik Schön published a slew of papers — all retracted later — in 2000 and 2001 claiming, among other things, that he had found evidence of certain organic molecules displaying superconductivity. A more recent one is centred on the Sri Lankan physicist Ranga P. Dias (currently working in the U.S.). In 2022, Nature retracted his paper, published in 2020, after independent experts spotted flaws in the experimental data. Last week, Physical Review Letters said it had decided after an internal investigation to retract another paper, not about superconductivity, coauthored by Dias.
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Chart 4 | The chart shows a timeline of papers related to superconductivity that have been retracted (including those that claimed the creation of a superconducting state, described applications based on such materials, and characterised known superconducting states) in 1991-2022.
Finding a room-temperature superconductor remains one of the toughest quests for physicists because it is so easy to make mistakes. This is why the new ‘exciting’ claim from South Korea will not be accepted until independent verification.
mukunth.v@thehindu.co.in
Source: Retraction Watch database, “Structural investigation of La(2-x)Sr(x)CuO(4+y) - Following staging as a function of temperature” and various other papers
Also read |Making sense of the room-temperature superconductor claim from South Korea
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