Sep 20 2016

Room Temperature Superconductivity – Not Yet

superconducting-trainI first remember really being interested in superconductivity in 1986, the same year many people probably first heard about it. Prior to that superconductivity, a property of matter in which electricity conducts without resistance and therefore without energy loss, was an obscure notion in physics.

In 1986, however, Alex Müller and Georg Bednorz, researchers at the IBM Research Laboratory in Rüschlikon, Switzerland, created a ceramic conducting material that was superconducting at the relatively high temperature of 30 K (-243 C). Prior to that the record was held by a vanadium-silicon alloy at 17.5 K.

Suddenly all the popular science magazines were filled with images of supermagnets, with headlines about the new science of ceramic conductors, of “high temperature” superconductors, and what the eventual goal of room temperature superconductors will mean for modern technology. Here we are 30 years later and I’m still waiting.

I also now have a much more developed sense of how technology advances, and how the popularizing of technology is often over-hyped and distorted. I was made to feel by the reporting that room temperature superconductors were inevitable and just around the corner. History has shown, however, that such predictions are highly problematic. Advances often take longer than we think, and progress tends to be sporadic rather than linear.

There are also different kinds of claims. Superconductivity is plausible but we don’t yet know exactly how to achieve this goal, so it is unpredictable. Fusion reactors are also plausible, yet there are significant technical hurdles that will likely take decades to overcome. Cold fusion is implausible, and I’m not holding my breath. Flying cars are not impossible, just massively impractical and I will likely never own one.

Every technological promise has to be evaluated on its own merits, will likely take longer than you think to be realized, and is difficult to predict.

Back to Superconductivity

So where do we stand now with superconductivity? Our understanding of superconductivity is advancing but remains incomplete. The current dominant theory of how superconductivity works is the BCS theory, named for John Bardeen, Leon Cooper, and John Schrieffer.

The basic idea is that in some materials electrons are made to combine into pair, called Cooper pairs. Normally electrons repel each other because of the like charge. However, in certain materials with a lattice structure vibrational energy can be transferred from the lattice to the electrons, which creates a weak bonding energy between the electrons.

The reason that temperature is important is because increasing thermal energy increases the energy pulling the electrons apart, and quickly overcomes the weak bonding energy of the Cooper pairs. The idea of high temperature superconductors is to create material that results in a higher bonding energy between the Cooper pairs so that they can stay together at higher temperatures.

Cooper pairs are important because they behave more like Bosons, rather than free electrons which behave like the Fermions they are. The pairs can therefore move through the material without interacting the way electrons do, therefore not creating any resistance or loss of energy.

Further, the BCS theory covers only certain kinds of superconductors. Certain copper-oxide materials have achieved superconductivity at 133 K (164 K at high pressure), but appear to be a different kind of superconductors we don’t yet understand.

The current record for high temperature superconductors was achieved last year in a metallic hydrogen, with superconductivity at 203 K (-70c).

One bit of good news is that there apparently is no theoretically upper limit to high temperature superconductivity through the BCS model. We just need to figure out how to make material that will achieve higher temperatures. Researchers are working on just that problem, and are making progress. They are figuring out what features materials need to have in order to create high temperature superconductivity.

There are some important milestones to keep in mind. Liquid nitrogen has a temperature of 77 K (-195c). This was achieved in 1987, with a variety of the ceramic superconductor discovered just a year earlier, when Müller and Bednorz at the University of Alabama-Huntsville substituted yttrium for lanthanum and achieved a superconducting ceramic at 92 K.

While this is still very cold, getting above the temperature of liquid nitrogen was a huge advance. This means we can make superconducting electronics that only need to be cooled with liquid nitrogen, which is readily available and affordable. This was part of the reason for huge optimism at the time, as advances seemed to be coming quickly.

As you can see, advances continued to be made, and we are now up to 203 K. The next big milestone is 273.15 K, or 0 C, which of course is the temperature at which water freezes. That is the definition of “room temperature” when referring to room temperature superconductivity.

At this point, however, every advance is of practical significance. We are getting close to the point where conventional freezer technology can achieve superconducting temperatures. We also have to consider the material itself – can we make wires and stuff out of it, and is it cost effective?

Let’s say we get to the point where we have an affordable and practical material that superconducts at -40 C, the temperature of a high end freezer. Now any business could theoretically own a superconducting appliance. If we get to -20 C we may be entering consumer-level applications.


We have been making steady incremental advances in our understanding of superconductivity and our ability to create superconducting materials. We crossed an important threshold about 30 years ago, getting above the temperature of liquid nitrogen. This created a tremendous buzz about superconducting materials, and also a bit of an unrealistic expectation of rapid progress to room temperature superconductors.

This is a pattern I have now seen many times. There is some early progress into a new technological field. This creates excitement and a spasm of science-fiction speculation about how this new tech will transform our lives.

These unrealistic expectations are not met, and eventually the technology falls off the radar, at least as far as the popular culture is concerned.

Meanwhile, the slow plodding course of scientific advance continues over decades. Then, several decades later, the technology crosses another milestone and suddenly we have all the benefits we were promised a generation ago.

This may take 30 years, or 60 years, or more (or perhaps never), but it does often happen. I was promised the internet in the 1970s, but had to wait 30 years for it to be fully realized. I was promised smart phones in the 1980s, but had to wait about 25 years. I was promised an all-electric car in the 1980s, and we are just now making that transition.

Enthusiasts in the 1950s were promised a flying car, and their children are still waiting.

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