August 5, 2023: Superconductors
Good evening. There is much enthusiasm right now about a claim of a functional room-temperature, ambient pressure superconductor. I briefly discussed the matter last week, and now I think the matter is worthy of a more detailed discussion. We will look at some history and theory behind superconductivity, some actual and potential applications, issues surrounding the recent claims, and conclude with some thoughts on what to expect going forward.
I might start with this article from Mishkat Bhattacharya on The Conversation explaining how superconductivity works in layperson-friendly terms. In conductivity, electrical energy is transmitted though the motion of electrons through a material. In ordinary conductivity, electrons move chaotically, and sometimes they collide with atomic nuclei. This dissipates energy as heat, and it is the reason why most conducting materials—space heaters, incandescent light bulbs, microprocessors, etc.—get hot. In superconductivity, the motion of the electrons is in phase with the motion of nuclei in such a way as to avoid collisions, so no energy is dissipated. This is very nice, but superconductivity typically requires low temperatures and/or high pressure to maintain the necessary conditions.
Superconductivity was discovered by the Dutch physicist Heike Kamerlingh Onnes in 1911. Theoretical work to understand the phenomenon led to the BCS (Bardeen, Cooper, Schrieffer) theory in 1957. It was not believed that a superconductor above the temperature 30 Kelvin (-243 Celcius) was possible until 1986, when such a material was discovered. The material is lanthanum barium copper oxide, which superconducts up to 35 K. It was discovered the following year that the critical temperature could be raised to 93 K by substituting yttrium for lanthanum. Among confirmed materials, I believe the state of the art right now is a lanthanum hydride, with a critical temperature of 250 K, though it requires extreme pressures. There is very great interest in developing a room temperature (above the freezing point of water, 273 K) superconductor that operates at “ambient” pressures (e.g. thousands of atmospheres, not millions).
Superconductors have many uses today already. A room-temperature, ambient pressure superconductor might greatly expand these uses, as expensive cooling equipment would no longer be necessary. Here is a non-exhaustive list of applications.
The largest commercial use for superconductors (about 80%) is (nuclear) magnetic resonance imaging (MRI), and the largest component of the cost of an MRI machine is the superconducting magnetics. A strong magnetic field, which can only be generated with superconductivity, is needed for imaging. The most commonly used material is NbTi (niobium titanium).
A magnetic field generated by superconductors—again, typically NbTi—is needed for magnetic levitation (maglev) trains. Due in large part to the cost of superconductors and the cooling systems, maglev trains are too expensive to go beyond a handful of high-profile projects. Maglev promises higher speeds and better energy efficiency over conventional rail by avoiding the friction of contact with the track.
About 5-10% of electrical power is lost due to resistance in power lines. This loss could be eliminated with superconducting wires. For the same dimensions, a superconductor can transit 200 times the power as a copper wire. Superconducting wires would also be more resistant to extreme weather and catastrophic events than copper wire. However, the cost of cooling render superconducting wires impractical outside of a few demonstration projects, such as in the Chicago area.
Superconducting qubits are one of several types of qubits used in quantum computing. They require elaborate cooling systems, such as a dilution refrigerator, which is an obstacle to commercialization quantum computers.
For classical computers, waste heat from resistivity is a bottleneck to faster machines. There was recently a demonstration of using superconductors instead of semiconductors. The research showed a clock speed of 770 GHz, far faster than conventional computers, and an estimated 50-100-fold improvement in energy efficiency. Once again, cooling serves as an obstacle to scaling up the technology.
Superconducting magnetic energy storage has niche applications on the power grid for short-term energy storage. A room-temperature superconductor would expand the use cases, and it might allow superconductor storage for a wider range of applications, including at the consumer level.
Strong magnetic fields are needed for magnetically-confined fusion, which is the dominant approach to fusion today and used by tokamaks such as ITER. Tokamaks generally use NbTi or Nb3Sn (Niobium-3—tin), and REBCO (Rare Earth Barium Copper Oxide) is envisioned for the follow-on DEMO fusion project. Superconductors for fusion are an active area of research.
Superconducting Quantum Interference Devices (SQUIDs) are devices for measuring magnetic fields with high precision. They have many uses, such as oil and gas prospecting, geothermal mapping, EEG and EKG (electroencephalogram and electrocardiogram) and other medical imaging purposes, mine detection, and other uses.
Superconductors to power railguns and coilguns are active areas of research. Looking farther down the line, a mass driver is a space launch system that accelerates a payload to orbital velocity through magnetic propulsion, not fundamentally different in concept from a maglev. Better superconductors would obviously be very helpful here too.
Superconductors are under exploration for RF filtering and microwave filtering, to enable more precise signal processing.
Permanent magnetics are suggested for radiation shielding for crewed interplanetary voyages.
NbTi superconducting wires are used at the Large Hadron Collider.
I hope it is clear that a room temperature, ambient pressure superconductor would be a very useful invention. However, it must be stressed that even if such a superconductor is verified, these applications do not follow automatically. Much depends on how expensive and difficult it is to manufacture the material, and each application is associated with its own additional significant engineering challenges. This is where I think the enthusiasm about room temperature superconductivity falls off the mark, and why the impact of such an invention will not be as immediately transformative as some people imagine.
With that said, we again come to the claim of Lee et al. to have developed a lead apatite material, LK-99, which purportedly has the desired properties. But there is reason to be cautious, given the history of faulty claims of room-temperature superconductors. I wrote the following last week.
There is a new claim this week of a room temperature superconductor. While such an innovation would have many useful applications, most of the press’ reaction has been skeptical because many similar claims have come and gone over the years. One of them is from the researcher Ranga Dias, which was retracted. Dias later made a second claim which is in doubt. There was fraud from the German physicist Jan Hendrik Schön, who claimed, among other things, to have developed a superconductor with organic materials. All his claims were withdrawn. There was another claim in 2018, around which there are allegations (not proven as far as I know) of fraud. The same researchers released more data in 2019, and I am not aware of any activity since then.
Since then, there have been at least three attempts to replicate the work of Kim et al. of which I am aware. This paper by Sinéad Griffin from the Lawrence Berkeley National Lab is one such attempt and is encouraging. This paper is also encouraging. And here’s an announcement in Chinese (article in English) from a research team finding superconductivity, though not at room-temperature yet, in LK-99. Still, these results are very preliminary. Manifold Markets has that the result will replicate by 2025 trading at 36% as of this writing, meaning that investors collectively assess a 36% chance.
I’ll keep an eye on this in the coming months. LK-99 might go the way of earlier room temperature superconductor claims, but I very much hope to see a positive outcome.
Quick Hits
Once again, the Institute for the Study of War has discussed the situation in Niger in some details in their latest weekly Salafi-jihdai update. There are several potential scenarios for how the coup plays out, all of which are bad. One such scenario, as ECOWAS (Economic Community of West African States) is considering, would be military intervention in Niger. While ISW is clearly not pro-coup, they regard such an intervention as a bad idea and one that would be a shot in the arm for terrorist groups in West Africa.
The New Atlantis has a piece, “Culture War as Imitation Game”, from Luke Burgis. The piece discusses the work of the French social theorist René Girard and how his model of mimetic desire is applicable to contemporary partisan politics. The piece is interesting but far from convincing. For example, at one point Burgis states,
Internal models of desire are inside of our world, and so the imitation can become reciprocal. There is the possibility of escalation. This, in my view, is the most dangerous thing that social media has done to our collective psyche and the reason why mimetic rivalry is so widespread today. Nearly overnight, the Internet put us all inside one another’s heads as internal models of desire — whether positively or negatively.
Here Burgis explains the mechanism by which social media drives political polarization. The idea that social media drives polarization, even if we are not sure exactly how, is one of those ideas that we all know to be true but for which the evidence is scarcer than one might think.