Experts studying superconducting substances explain why ``zero electrical resistance = superconducting substances''
A research team at the Quantum Energy Research Center, Korea University, has published a paper that ``
I am seeing a lot of newcomers lately to the room-temperature superconductor rodeo.
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
They might not be aware of the long history of these events, and I think there's some cross-cultural communications difficulties going on because of that.
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Superconductivity is a state in which the electrical resistance of a material becomes zero. In general, the electrical resistance of metals increases when heated and decreases when cooled, so it has been thought that this can be achieved at low temperatures.
What is superconductivity? And what is 'LK-99' that realizes superconductivity at normal temperature and pressure & Summary of results of reproduction experiment - GIGAZINE
Professor Fuller first said, ``There is no reason why superconductors cannot exist at room temperature,'' but ``I don't know how to make room-temperature superconductors.'' Moreover, even if a normal temperature and normal pressure superconductor exists,
It does not have a phonon-mediated BCS mechanism. The BCS mechanism is a superconductivity generation mechanism proposed in 1957, and phonons are quasiparticles closely related to conventional superconductivity. In other words, Professor Fuller points out that although a normal temperature and pressure superconductor can theoretically exist, it will be due to a different mechanism from the typical superconductors identified so far.
There's no reason (that we know) that a room-temperature superconductor can't exist.
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
But we also don't know how to make one by design.
It almost certainly won't superconduct by a “conventional” (ie phonon-mediated BCS) mechanism.
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PS, in tweet 2, I should have specified that a room temperature *ambient pressure* superconductor almost certainly won't have a phonon-mediated BCS mechanism.
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
(It could happen at high pressure, though recent reports are also colorful.)
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For this reason, it is thought that superconductivity will be found by chance in unexpected and strange substances. However, it seems that not all ultra-low resistance states discovered by chance are superconducting.
So it'll be a serendipitous discovery in some unexpected strange material.
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
But not every serendipitously unexpected apparent very low resistance state in a strange material is superconductivity!
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As mentioned above, superconductivity is a state in which the electrical resistance of a material is zero. In other words, Professor Fuhrer says that `` if the electrical resistance is measured and it is zero, it is superconducting '' ... but in reality it is not so, and there is `` deception ''.
You'd think superconductivity would be easy to detect; it comes with zero electrical resistance, so if you measure resistance, and it's zero, you're done. Unfortunately there are many ways to get fooled (too many for one thread!)
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
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For this reason, whether or not a material is superconducting is confirmed not by ``whether or not the electrical resistance is zero,'' but by multiple factors such as the Meissner effect and AC magnetic susceptibility .
So generally you'll see multiple pieces of evidence for superconductivity in a new report: Meissner effect, AC susceptibility, temperature-dependent critical field and critical current, single-particle tunneling gap, jump in specific heat at T_c, Josephson tunnelling...
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
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Still, the natural world can fool researchers. Due to the unexpected high temperature of the result, which is difficult to explain and resembles superconductivity, it is often described as 'suggestive' or 'unidentified superconductor'.
Even then, nature sometimes throws good scientists a curve ball, and can fool on multiple counts. So there is a steady trickle of difficult-to-explain results that look a lot like superconductivity, sometimes at unexpectedly high temperatures.
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
“Tantalizing” is often used.
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These are colloquially called Unidentified Superconducting Objects.
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
(I've heard a few scientists credited with originating that phrase; Bob Cava credits Koichi Kitazawa in the linked paper). https://t.co/TgR47DNn43
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Below is a video showing diamagnetism at room temperature, which seems to be room temperature superconductivity.
Giant Diamagnetism in Au-Ag Nanostructures at Ambient Conditions-YouTube
This video is an experiment involving a reliable scientist, but Professor Fuller points out that 'superconductivity' research that is suspected of fraud is also being conducted.
There are also some more scandalous cases where fraud was known to occur or strongly suspected. But AFAIK the examples above aren't scandals*, and reputable scientists were involved.
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
*Some may disagree. Let's just say that there are probably many genuine reports out there.
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At first, these stories seemed credible, but there were many uncertainties about how they ended, and there was no news that the experiments had been replicated at other laboratories. It is said that there are cases where there is no news.
Also notable is that there's no clear end to each of these stories; in many cases if you look into these past examples, you'll find them just as credible as the most recent example. of experimental replications in other labs...
— Prof. Michael S Fuhrer (@MichaelSFuhrer) August 2, 2023
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