Oct 16 2020

Room Temperature Superconductor

Once again we have the reporting of a technological advance but leading with a bit of hype. The BBC headline is – “Superconductors: Material raises hope of energy revolution.” (Original article) I would first point out that I have been reading similar headlines since the 1980s. No revolution so far. We see some version of this claim every time there is an incremental advance in superconductor technology. We have hit a bit of a milestone with this latest progress, but it has to immediately be put into proper context.

Scientists have indeed demonstrated the first room temperature superconductor. But you know there’s a catch, right?

The scientists observed the superconducting behaviour in a carbonaceous sulphur hydride compound at a temperature of 15C.

However, the property only appeared at extremely high pressures of 267 billion pascals – about a million times higher than typical tyre pressure. This obviously limits its practical usefulness.

“Limits its practical usefulness” is perhaps a bit of typical British understatement. The way I see it they have just substituted one highly impractical limitation of superconducting material (extreme low temperatures) with another (extreme pressure). The research could have easily gone the other way. What if the high pressure superconductors were discovered first, then the holy grail would have been finding a superconductor at normal pressures, which they could have done by using extremely low temperatures. In fact, the low temperature may be the easier of the two.

At atmospheric pressure the record is still held by cuprates, which have demonstrated superconductivity at temperatures as high as 138 K (−135 °C).

It is easier to cool something to -135 °C then to put it under 267 billion pascals of pressure, so you might even argue we have taken a step backwards. This still might be useful if the research leads down a new path that ends with room temperature and atmospheric pressure superconductivity. Perhaps we’ll see in another 30 years.

To add a bit of background, superconductivity refers to the property of a material in which it provides zero resistance to the flow of a current. This means it does not heat up at all, which bleeds away energy and is therefore a huge source of inefficiency. Our civilization is largely electrified, so making all electrical devices more efficient could be a huge boon. Also having small electronic devices that do not heat up would also be highly useful.

How does superconductivity work? The prevailing theory is called the BCS theory after John Bardeen, Leon Cooper, and Robert Schrieffer. This involves electrons forming into pairs which are called Cooper pairs.

Pairs of electrons can behave very differently from single electrons which are fermions and must obey the Pauli exclusion principle. The pairs of electrons act more like bosons which can condense into the same energy level. The electron pairs have a slightly lower energy and leave an energy gap above them on the order of .001 eV which inhibits the kind of collision interactions which lead to ordinary resistivity. For temperatures such that the thermal energy is less than the band gap, the material exhibits zero resistivity.

One way to get the thermal energy less than the band gap is to supercool the material. But in recent years researchers have found that certain materials can form superconducting structures at extremely high pressure as well. The researchers hope to “tune” these chemical structures to allow for room temperature superconductivity at normal pressure.

Of course general reporting of this study spends most of its time recounting all the ways that superconducting material would be awesome, and it would be. But this same list has been dangled in front of the public for over 30 years, basically my entire adult life. Superconductivity, as a result, has entered the realm of flying cars and robot butlers – a denizen of the poorly defined “future”. At this point I no longer get excited about the latest superconductivity “breakthrough”. I suspect that I will never see real room temperature superconductivity at atmospheric pressure (and without some new extreme limitation) in my lifetime, and perhaps it will just turn out to be one of those things that is simply not possible. There can always be an unexpected breakthrough, but I am no longer holding my breath.

I categorize theoretical future technology in several ways. There are those things, like practical superconductivity, which are theoretical but we don’t know if and how they are achievable. They may be possible, but we may never achieve them. It is not just a matter of continued incremental advances – we need new and unpredictable discoveries.

Then there are those technologies which are also not impossible, just impractical with current technology. I put flying cars in this category. I think we will eventually have them, it’s just taking a lot longer than people suspected. Continued incremental advances will get us there. In fact, we may be finally getting somewhat close. I also put general AI into this category – possible, achievable with incremental linear progress, but taking a lot longer than futurists predicted.

Then there are things that are not impossible, but may never be practical. A space elevator, for example, is a sexy idea, but may never be worth the investment and risks. Jetpacks also fall into this category, at least for practical applications (not just recreation). I do wonder if fusion energy is in this category or the previous one. It is not impossible, but is very difficult to achieve, and the question is – by the time we do achieve it, will it be cost effective? It might simply be eclipsed by other technology.

We also have alleged technology that I think is impossible and will always remain in the realm of fantasy. Cold fusion and any form of free energy fits into this category. Faster than light travel probably does as well, along with antigravity and Star Trek style teleportation. But there is a gray zone to this category as well if we consider extreme timeframes. Sure, some things break the laws of physics and are forever impossible. But some technology in this category may be impossible, but also may be possible with extreme technology, millions or more years advanced beyond where we are now. This amounts to finding loopholes in a deeper understanding of the laws of the universe than we can’t even guess at currently. Such technology fits the words of Arthur C. Clarke -“Any sufficiently advanced technology is indistinguishable from magic.”

Practical superconductivity may, in fact, be in this last category – impossible for now, but theoretically achievable by extreme technology beyond our current imaginings. I guess we’ll see.

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