In Our Time - Superconductivity

Episode Date: February 23, 2023

Melvyn Bragg and guests discuss the discovery made in 1911 by the Dutch physicist Heike Kamerlingh Onnes (1853-1926). He came to call it Superconductivity and it is a set of physical properties that nobody predicted and that none, since, have fully explained. When he lowered the temperature of mercury close to absolute zero and ran an electrical current through it, Kamerlingh Onnes found not that it had low resistance but that it had no resistance. Later, in addition, it was noticed that a superconductor expels its magnetic field. In the century or more that has followed, superconductors have already been used to make MRI scanners and to speed particles through the Large Hadron Collider and they may perhaps bring nuclear fusion a little closer (a step that could be world changing).The image above is from a photograph taken by Stephen Blundell of a piece of superconductor levitating above a magnet.With Nigel Hussey Professor of Experimental Condensed Matter Physics at the University of Bristol and Radbout UniversitySuchitra Sebastian Professor of Physics at the Cavendish Laboratory at the University of CambridgeAndStephen Blundell Professor of Physics at the University of Oxford and Fellow of Mansfield CollegeProducer: Simon Tillotson

BBC Sounds, music, radio, podcasts. Thanks for downloading this episode of In Our Time. There's a reading list to go with it on our website, and you can get news about our programs if you follow us on Twitter at BBC In Our Time. I hope you enjoyed the program. Hello, in 1911, the Dutch physicist Haika Kamaling-oners made a remarkable discovery that nobody predicted and that none can since fully explain. It's called superconductivity.

When he lowered the temperature of mercury close to absolute zero and run an electric current through it, he found not that it had low resistance, it had no resistance. A century later, and this has already been applied to make MRI scanners and to speed particles through the large Hadron Collider and may perhaps bring nuclear fusion a little closer, a step that would be world-changing. With me to discuss superconductivity are Nigel Hussie,

Professor of Experimental Condensed Matter Physics at the University of Bristol and Radbao University. Sushitra Sebastian, Professor of Physics at the Cavendish Laboratory at the University of Cambridge. And Stephen Blundell, Professor of Physics at the University of Oxford and Fellow of Mansfield College, Oxford. Stephen Bundell, can you take us into the laboratory of Camerling Ones?

What had he been working on to get to this point? Well, Cameling Onis was on a scientific quest to understand how various gases can be liquefied. The issue is that we know that water is a liquid, but nitrogen is a gas. And why is that? It's to do with the interactions between the molecules. And in nitrogen, the interactions are rather weak, and so at room temperature, nitrogen is a gas. To turn nitrogen into a liquid, you have to cool it down.

Now, in understanding this, you can start with Boyles Law from the 17th century, which only describes gases, and Boyle's Law doesn't contain within it the idea that something can liquefy. So to take that further, one of Honest's mentors, Van de Velsz, had come up with an equation which describes an improvement on Boyle's Law,

showing how gases can be liquefied when you cool them down. And Honest wanted to, Camling Honest wanted to check that out experimentally. And he was on a quest to try and liquefy the gases that had not, not been liquefied before his time. And the particular one he was trying to do was helium, because that was the last gas to be liquefied. He succeeded in 1908 in doing this. He was in a

competition between James Dewar, who was his leading rival here in London. Camling Arnis had the great advantage that he had trained a bunch of technicians. So he had a small army with him who were making bits of apparatus, and that gave him the edge. And so in 1908, he was the first one to liquefify helium. That gave him the first laboratory in the world that could get to temperatures of just a Kelvin or 2 above Absolute 0. And that opened up a new frontier. What does a Kelvin or 2 mean to most people? So Absolute 0 is the lowest temperature that we can get.

It's minus 273 degrees centigrade or Celsius. And a degree Kelvin is the same as a Celsius, but you start your 0 at minus 273. I see. Was there anything of the sort of accident or fluke about this? Well, not in the discovery of liquid helium, but once he had this new technique of being able to get down to very, very low temperatures, he then had a new frontier to explore. And that was the point where serendipity occurred, because what do you do when you have this new technique, being able to take things to a lower temperature than anyone can do? His first idea was maybe he could solidify helium. Unfortunately, that didn't work, as we now know that helium doesn't solidify under atmospheric pressure.

So the next thing he tried was to look to see what happens to the resistance of materials when you cool them down. And he tried this with platinum, which is a very good metal. And one of the possibilities might be that the resistance, the electrical resistance of a metal, which was known to decrease when you cool materials. One possibility was that it might rise at very low temperature because the electrons would freeze. That was Lord Kelvin's idea. But he found, in fact, it was quite different. the resistance fell and fell and fell and fell and eventually plateaued.

And he realised that the reason that it plateaued was because his platinum wire wasn't perfectly pure. So he realised that if you really wanted to understand what happens to the low temperature properties of materials, he had to make a really, really pure metal. How do you do that? So he came up with the idea of distilling a liquid metal and he thought of mercury.

Mercury is a liquid metal. Let's distill it like we distill whiskey, get all of the impurities out. Then we'll have something incredibly pure. He cooled down his pure distilled mercury. What he found was that below about four degrees above absolute zero for Kelvin, the resistance just vanished, just completely disappeared. What resistance are you talking about to remind the listener?

This is the electrical resistance. So all metals have a resistance. This is why when you use your cattle element or your toaster, you pass an electrical current through a wire and it gets hot because of electrical resistance. and in Mercury's case, once you get it below 4 Kelvin, that resistance just vanishes, which means you can suddenly have a current flowing with no battery, because the current will flow all by itself. So, Shetra, what was surprising about this?

So as Stephen mentioned, and I think all of us have encountered this many times, quite often you expect certain physical behaviour. So in this case, what was expected. was that the resistivity as the temperature was lowered of metals would rise because they would stop flowing. So the electrons would stop flowing. They would sort of freeze when they got to low enough temperatures and the resistivity would go up again. So it was a big shock when instead of going up, the resistivity completely disappeared. And what was shocking about this was that it didn't just gradually disappeared, wasn't that it became better and better of a metal.

It just transformed into a completely different entity, which was a superconductor. And one of the ways in to think of this is to recognize that a superconductor is a different phase of matter from a metal. And so we can think of, say, I think of, say, I think, water and steam, these are all different phases of the same chemical compound. So we have very different behaviors. And within each regime, so within a phase that's ice, you can predict the behavior, you know what might happen as you raise the temperature, as you change the properties. But then it reaches a precipice. So if you take water and you increase the temperature, it reaches this precipice, which is a transition where this phase that is water dramatically transforms into a

different phase, which is steam. And the properties of each of these phases are dramatically different. You cannot anticipate the behavior of one of these phases of matter based on the other. And in this way, when resistivity disappeared completely, this was a shock that was a signal that a new phase of matter had been discovered, and this was superconductivity. It wasn't a better metal. It was a completely different entity. What was your reaction to that? I think that when superconductivity was discovered, initially it was the properties of resistivity,

which were thought to be important. So the resistivity vanished as you went to lower temperatures. but I think as other properties of superconductivity was discovered, for example, that it expels magnetic field lines, it levitates magnets. So it throws the magnetic field out of the... Exactly. So if it were a metal and you brought a magnet near it, the magnetic field lines would go through the metal. And in this case, one of the really shocking things about the superconductor

is that it doesn't allow the magnetic field lines. to penetrate. And I think it was at this point that one of the recognitions occurred that this was a new phase of matter and what's one of the really important things about it is that the electrons in a superconductor are collectively behaving in a different way.

All of them together are doing something very different that you can't just understand in terms of individual electrons. Superconductivity is also something that really gets the imagination going. Because when you see, and every time I do this experiment to show students, you get a superconductor and you levitate it over a magnet. I've seen this countless times,

but every time I'm amazed and have this sense of awe and wonder. Because how on earth can a thing levitate in the air? And yet it does. And this is because of this rather extraordinary, almost mystical property that I think... Why is what to be mystical and magical? I mean, of course, we know it isn't, we know it isn't mystical and we know it isn't magical. Well, it isn't magic, but it is magical, I think. It has that sense of wonder and awe-inspiring generation, I think, that we all feel.

This is unpredictable at the time. Is there a sense of which unpredictability is important in the development of this? Yeah, absolutely. And all of us are condensed matter physicists, and all of us are very familiar. with this idea that collective behaviors in condensed matter, so we're dealing with materials that comprise trillion trillions of electrons, so 10 to the power of 23 electrons. And when these electrons come together in collective behavior,

the behavior that emerges is radically different from that of individual electrons. So while you might understand very well how individual electrons behave, when trillion trillions of electrons come together and new behavior emerges, you have no idea what's going to emerge. And most of the time, actually all of the time, it's beyond what you could imagine. It's not just that you don't know which option it's going to pick.

You have no idea. So superconductivity wasn't something that was conceived before it was discovered. And I think that's at the heart of what we do as experimentalists. You have to go do the experiment. So as Stephen was saying, it needed helium to be liquefied, to know. So it's that frontier. You go do the experiment and see what happens.

How else would you know this new phase of matter was even possible to occur? What do you do with trillions and trillions of electrons? I can't imagine it at all. When I'm talking to physicists on this program, the figures are so big that I can't imagine them or they're so small that I can't imagine them. But anyway, let's talk about the trillions of electrons. Yeah, actually, this is the number of stars in the visible universe. And this is in, say, a milligram of material.

So it's quite incredible. We're working with milligrams of material. But the number of electrons in such a tiny amount of material is, if you look up and look at, you can't even imagine the stars in the visible universe. But if you could, that's as many as there are. electrons in a milligram of material. So what power does that give it? Power in terms of the electrons coming together.

So when you think of individual electrons, they're these sort of ghostly entities because they're really probabilistic waves. They don't have an extent. But when trillions trillions of electrons come together, they coalesce into an entity that takes on a corporeal form. So now it becomes a macroscopy. physical entity that you recognize actually can shape shift and take on many different forms. So, for example, ice, water, steam are different emergent phases, coal and diamond,

are different phases of the same material. And superconductivity is such an emergent collective phenomena, which we'll talk about has incredible applications as well as mind-blowing, physical behaviours we would not have expected or imagined from what we knew of single electrons. Thank you. Nigel, Nigel Husser. It's cider in Mercury, but the search was on for other superconductors. How far did they get and how fast did they get there?

Well, short answer is rather slowly. In fact, in Camelene Onis's own lab, he found that also tin and lead were superconductors. but other good metals like gold, platinum, copper, were not. And the main reason why progress was slow at the beginning was basically due to the difficulty of accessing these low temperatures. In fact, the Leiden Laboratory was really the only laboratory in the world that had liquid helium in sufficient quantities

to be able to do these kind of experiments. But eventually over time, in other laboratories and other countries, managed to catch up. And so many more superconductors were then discovered and many more of the remarkable properties of superconductivity were then discovered. But as I said, progress was slow. And really, I think probably the biggest contributor to this endeavour was a German-born physicist called Berndt Matthias,

who is said to have discovered more superconductors than any other scientist. And in the process, Matthias came up with a set of, empirical rules to help others in the search for new superconductors. And they included advice such as stay away from oxygen, stay away from magnetism, stay away from insulators, and lastly but rather ungenerously, stay away from the theorists. And this served him extremely well, these rules, and in fact led to him reaching the maximum superconducting transition temperature at the time. which was of 23 Kelvin in an intermetallic alloy in 1973.

So if you think about back to the discovery in 1911, so it's taken six decades to go from minus 269 degrees Celsius to minus 250 degrees Celsius. So, I mean, on an absolute temperature scale, that was significant progress. But if you think about the quest of trying to see superconductivity at room temperature, it seemed that we were never going to reach that. And it really was only with the remarkable discovery

made by Bednors and Muller in 1986 that that whole prospect, that whole dream of high-temperature superconductivity was realised. Was that another accident, that discovery? If you ask Alex Muller and George Bednors, they would say no. They were, in fact, looking for new superconductors. And they had seen previously that, in fact,

Despite what Matthias had recommended, there were certain oxide materials that were showing signs of superconductivity. And so Bedno Zemullah decided to focus on a particular type, which did indeed contain oxygen and made the breakthrough. Can you tell us more about the part that magnet isn't played in this? In addition to this remarkable property of perfect conductivity or zero resistance, as Soutitra said, the other distinguishing feature of superconduct is its ability to exclude magnetic field from its interior. Why is that, is that a virtue? Well, it's what it is, isn't it? So there you go.

Yeah, but we know from the very early works of Michael Faraday and Emil Lenz that if you change a magnetic field above a metal, you induce currents on the surface, electrical currents, which flow and produce their own magnetic field, which actually flows in a certain direction. as to oppose the magnetic field that's trying to push its way through the superlector. Now, if you imagine bringing a magnet close to a superconductor, the currents that are induced are these super currents with no resistance. But the strength of the field that's produced completely counters the field that's been applied,

and so, indeed, you have a field-free zone inside the superconductor. Now, it doesn't matter whether you turn on the magnetic field at high temperatures when it's not a superconductor can call it down or turn on the magnetic field when it is a superconductor. The exclusion happens in both cases. And that is one of the reasons this was discovered by Meisner and Oxenfelt in the 1930s. And this property really told us, confirmed that this was indeed a new distinct phase of matter. And so the end result was the same, independent of the history, depending on how you got there, the end result of this exclusion of this magnetic field was the same.

And that really gave was this belief that the superconductor was a new state of matter. Thank you. Can we peg away at this, Stephen? It's been said that nobody can, yes, fully explain superconductivity. Could you be the first to explain it? Well, I can maybe trace out some of our understanding of how superconductivity works. Discovered in 1911 by Camer Onis, as we've said, the Meissener effect is 1931, so that's 20 years later. and theorists were trying to work out what was going on with superconductivity.

One of them, Felix Bloch, who is very well known for students who are studying solid state physics and who has a theorem named after him, he had a crack at the problem and got nowhere. So in fact, he came up with a theory which was superconductivity is impossible. That was his statement because he was so frustrated with the lack of progress that he'd made. I think the key insight that began to give you a clue as to what was going on was done by, Fritz and Heinz London. These are two physicists working in Oxford in 1930s. Fritz and Heinz had both come over to Britain as part of the exodus of German Jewish scientists. Frederick Linderman in Oxford had managed to get out a lot of scientists from Germany with Jewish backgrounds in

the early 1930s when things were getting too difficult for them. Einstein and Schrodinger both came to Oxford. Einstein didn't stay, but Schrodinger did. and Fritz and Heinz London were two of these. These two brothers decided when they were in Oxford, where there was now this beginnings of low-temperature research in the UK to try and tackle the problem of superconductivity. And it was Fritz London who had the particular insight as to what was going on. So he reasoned as follows,

if you take an ordinary coil carrying current, it has electrical resistance. That means you need something to power it. You need a battery. or you need some other power source to keep the current going round and round. But in a superconductor, the current will just go round and round forever. And Fritz London thought, well, that's just like an atom. Because in an atom, you have a positive charge with electrons going round and round, and there's no battery in an atom.

The current goes round and round forever. So Fritz London reasoned, or maybe a superconductor is a giant atom. This coil of wire, which could be a few centimetres across, or in an MRI magnet it might be a metre across, Maybe that's a giant atom. Now, why is it the electrons in an atom go round and round forever? It's because they are in what we call a quantum coherent state, a wave function, a beautiful wave function that is defined by quantum mechanics

and whose property, whose very nature is to go round and round forever. It's just an element of reality. And maybe in a superconductor you've got exactly the same thing. So Fritz and Heinz put equations together to try and describe that, and they produced the Meissner effect. this thing that both Nigel and Situytra have talked to us about. So suddenly you had a clue, maybe superconductivity is something about this quantum coherent effect on a macroscopic scale. Sashitra, can you bring in the trillions again and say, how did they figure now that we've moved on?

Yes, so if we think of individual electrons in a metal, so they're traveling along, they're carrying current, they're bumping into each other, bumping into atoms and losing energy as they travel. What's very different in a superconductor is that you can take meters, kilometers of a superconducting wire, send current through it, and it's perfect. There's absolutely no resistance. You'll get out of the other end exactly how much you put through. You can take a ring of superconducting material, put current through it. It will flow for the age of the universe. So this is telling us something very special, and it's telling us that the electrons have stopped,

behaving as individual entities, so they're not bumping into each other, bumping into the atoms, but they've coered. They've clicked into this macroscopic entity, which you no longer think of as made up of little bits reducing them to individual electrons. And it is as fundamental a quantity as these electrons. For instance, if we were to say think of something like consciousness, it would be unimaginable that you try to understand consciousness by cutting up, cutting up the brain into little bits and saying, okay, from which piece or from which neuron do you get consciousness?

You recognize it's a different entity. Different behavior has arisen in this macroscopic ensemble, this collective of entities has self-organized to give you very different behavior. And it's in a similar way that we need to think of, such emergent collective behavior that together you get a new macroscopic entity forming that cannot be reduced into bits to say we're going to make like a Lego bit out of it and figure out which bit is doing what aspect of this behaviour it's not it's a new collective entity which

can't be reduced and what is the significance of that the significance is that in emergent forms of matter you encounter new physical behaviors that you could not encounter an individual electrons. So firstly, collective behaviors are dramatically different. Secondly, it's, again, the crucial aspect of experiment in discovering emergent phenomena occurs because, again, you cannot anticipate what type of emergent phenomena is going to occur until you go look, because we know what individual electrons do. We don't know what trillion trillions of electrons do until we go do an experiment to see what happens,

until then we couldn't have imagined it. Thank you. Nigel, where does the BCS theory come in? Well, the BCS theory, so named in honour of its three proponents, which were John Bardeen, Liam Cooper and Robert Shrefer, was really the first complete microscopic theory of supercom. and is widely regarded as one of the triumphs of 20th century physics. And, you know, thinking about this unpredictability and this surprising phenomena, remarkable phenomenon of superconductivity, it was quite remarkable that in the end these three were

able to provide a complete theory of how it works. And the basic premise of this attributed to Cooper is that the electrons, the inner superconductor, they pair up. Now, this might seem slightly odd because electrons are negative, charged and we know that like charges repel. So the idea of them partnering up like that somehow counterintuitive. And indeed, if you just squeezed a whole bunch of electrons

into an evacuated chamber, there's no way that they will pair up. But the electrons, the superliting electrons, they move within a lattice of ions. And ions are essentially the atoms that make, are the building blocks of our crystals. of our materials, and they've donated some of their electrons into this sea of conduction electrons that make up the metal. Now, having donated these electrons, they become positively charged. Okay, so now a sort of simple way to think of this of the BCS picture is you imagine an electron

moving between two rows of these positive ions. Of course, the electron being negatively charged momentarily attracts those positive ions. But those ions are so much heavier than the electrons, they don't reflex back immediately. So they kind of linger in that state. And this creates then a cloud of positive charge that a second electron gets attracted to. Now, in being distorted,

the first electron has given up some of its energy. It's lost some energy. But when those ions relaxed back, they give back the energy that was lost by the first electron to the second. And so by pairing up in this way, the total energy of the electron system is conserved. And voila, you have perfect conductivity. Good God. Now, the development of this theory, you know, you couldn't do it by just thinking about a

single electron. You had to go back to the trillions and trillions of electrons that Cichita talked about. And really the tour de force that Barding, Cooper, and Schrefer did was to kind of use all the machinery of quantum mechanics in order to produce a theory which actually ended up explaining essentially all the known properties of superconductors at the time. I think for that reason, you know, it's recognised for the triumph that it was and gave the three people the Nobel Prize in 1972. Thank you. Stephen, what happened in 1986 that seemed to change everything? Quite a bit has been changed already, but what more happened?

So until 1986 we had this Bardeen Cooper-S-S theory that Nigel's described. And one of the predictions that seemed to come out of that theory is that you wouldn't expect to have a superconductor that worked much above 20 degrees above absolute zero, so about no higher than, let's say, minus 250 degrees. And none had been found higher than that temperature, so there didn't seem to be a problem. and Nigel's already mentioned the work of Bednaws and Mueller,

these two scientists working in an IBM research laboratory just outside Zurich trying to understand or trying to find a new superconductor. They had some what seemed to be crazy ideas. People had looked for superconductivity in elements, metals, in alloys. Bednorz and Muller were looking at oxides. Now, an oxide is usually a compound of a metal and oxygen, so something like rust, that doesn't look like something that's going to conduct electricity. So Bednors and Muller were focusing on these oxide materials,

trying to look for superconductivity, and they had a hunch, they had a good lead as to why they thought this might be a profitable area, but nobody really believed them. And in fact, their motivation, one might still now question whether, in fact, it was completely nailed down. But they found a new material which superconducted at 30 degrees above absolute zero. Now once they'd done this and once they'd published it, other people looked at the chemical formula. First of all, they had to actually determine the chemical formula because Bednors and Mueller hadn't really tied it down.

And then what they thought of doing is let's make some chemical changes. Let's just substitute one atom for a very similar one. And very quickly, within months, the transition temperature, this critical temperature below which you see superconductivity, had gone from 30 degrees above absolute zero, 40 degrees, and then it leapt up to about about. 90 degrees above absolute zero. So suddenly within the period of a year or two, you had this extraordinary discovery of huge families of materials that looked like room temperature superconductivity was just around the corner. Now, this had a number of implications. First of all, it seemed to transform technology. But secondly, it put a big question mark over the BCS theory, because the

BCS theory had seemed to predict that you couldn't get high temperature superconductivity, and experimentally you can. So Jyre, again, this wasn't predicted. So what does that say to you? I really like the history of Bednods and Mullah for various reasons. I think one of the reasons I like it is because it has to do with materials. And I think condensed matter, superconductivity really is all about materials. And all of the things. And all of the things that. these emergent phenomena we talk about, trillions of electrons, macroscopic behavior. It all is happening inside materials. And these were materials chemists.

And they were looking at new materials. And another aspect I like about it is what Nigel was talking about, these so-called Mateus rules. Don't go near insulators. Don't go near magnets. Don't go near oxygen. And I love the heretical aspect that... Don't go near theories.

Yeah, don't go near fears, but I love the heretical aspect of Bednots and Mueller, who decided to do it anyway. And there were massive laboratories all around the world. There were sort of industrial production type efforts to look for superconductors pretty much close to what these rules were predicting. But Bednots and Mueller were actually in secret pursuing this search for superconductivity. And in his Nobel lecture, Mueller says that he had to keep it secret because otherwise people might think they weren't serious scientists.

I think their employees knew. Their employers knew. Yes. But I think that I think the idea is that as Steve was mentioning as well, the physics that they were thinking of might be driving this wasn't commonly held. and it still might not be the physics that's driving high-temperature superconductivity, but the idea of going up against what was commonly held, these rules that were so-called inviolable. I love this about the search because I think, and the idea that they had to do it without publicizing the program to the rest of the world because they might be considered to be not serious scientists,

I think that still happens. And I also love the fact that when they were on this quest to find a new superconductor, they kept, they looked in these perovskite oxides, and they kept finding insulators, but they kept going. I really like that because I think it shows this idea of experimenting to see what happens, looking at materials, tweaking their properties, and looking to see what might happen, because if it wasn't high temperature superconductivity they'd discovered, it might have been something even more exciting and exotic. It wouldn't have been a dead end. Nigel, can we go back to electromagnetics and how superconductors change that area?

Yeah, so electromagnets are essentially wound coils of copper through which hundreds of amps of current are passed and this creates then a magnetic field which can be about twice the strength of the strongest permanent magnet that we know of. Now, this, of course, having resistance, these electromagnets, it generates heat, and so we waste a lot of energy or use a lot of energy in order to create those magnetic fields. But with a superconducting coil, again, we come back to the supercurrent, we can have a current flowing with essentially no resistance, and so you can create a permanent magnet, which just stays there for all time.

And the only energy cost then is in charging it up or charging it down or also cooling the system. And in fact, this was Camelene Onus's original dream when he first discovered superclinativity that you could one day make strong magnets out of these elemental superconductors. As it turns out, these elemental superlactors turned out to be what's known as type 1 superclyluxes,

I guess because they were discovered first. And these type 1 superconductors can only support a modest current before super connectivity is destroyed. But then later, type 2 supergnexers were discovered. And these are actually able to support much larger current densities. And so now you could create magnetic fields,

which were like 10 times larger than the strongest permanent magnet. You could also make magnetic fields which are of the same size of same strength as a electromagnet, but much smaller. And so this led to a sea change in the design and manufacture of strong magnets for all manner of applications, such as the MRI scanners that you mentioned, ship engines, levitated trains, particle accelerators, and now nuclear fusion reactors. And so it's really that kind of original dream of onus which has finally been realized.

Stephen, where's it taking us now? Well, one of the new developments is to try and build a quantum computer using superconductors. So a conventional computer uses electrical circuits, classical circuits as we would call them, transistors switching on and off, giving us the ones and zeros that are at the heart of any computing system. In a quantum computer, what you want to do is not just have one or zero, but you want to have a quantum superposition of one and to zero, so it's like Schrodinger's cat, which is both alive and dead. Your bit of information can be both one and zero.

and you can't do that with an ordinary transistor, but you can do it with a superconductor because it's essentially a quantum object. So superconducting circuits can act as quantum bits of information. And so most of the current attempts to build quantum computers at the moment in various laboratories around the world are using superconducting circuits. And so that's one of the big advances that's happened within the last few years. So, Chitra.

More recently, applications, that are in use of, for example, very light motor, electrical motors, with gearless bearings, frictionless bearings used in electrical aircraft where you need very light weight motors in wind turbines. So these are already in use. Also... This all comes out of this research. Absolutely, yes.

So superconductors, the aspect of magnetic levitation, the aspect of carrying electricity without any loss. and what's amazing is that these are quantum properties. These are very fundamental properties that took 50 years for the theory to be discovered after the experiment, so they're really challenging quantum concepts to understand. But they're also physical, tangible. You put your head in an MRI machine.

So most of us have encountered superconductivity is not just something in a lab that scientists are peering over. And I think, as Nigel mentioned as well, one of the applications that is currently really exciting is nuclear fusion. And this is where hydrogen and hydrogen combined to give helium to create energy, in this case, create very, very hot plasma. So millions of degrees of Celsius heat is produced, which is transformed into electricity. But you need superconducting magnets to confine the plasma.

so you need magnetic field lines to confine the plasma. So the only way to make this nuclear fusion in order to create energy of reality is to have superconducting magnets. And this is technology that is being developed right now. And it's incredible that superconductors are, you know, still transforming so many aspects of everyday lives, of energy. And there's so much more to come. Stephen was talking about quantum computing.

superconducting electronics are transformational. We expect that at the moment, we think that digital means somehow data vanishes into a cloud. It doesn't really, it goes into data centers. There's carbon footprint, which is almost as big as the airline industry. But superconducting electronics, again, will transform that and make that very low emission. So all aspects of our lives are being touched by superconductivity.

I think, you know, we're now at a point where, of course, you know, we would, we've, as Steve alluded to, you know, we've now got superconductors that display all their remarkable properties, but you only need to cool them in something like liquid nitrogen as opposed to liquid helium. Now liquid nitrogen is, you know, 10 times cheaper than helium. It's plentiful, of course, you know, makes up most of the air around us. And so very, you know, what I guess one of the most exciting prospects then is that we could access all of this kind of on the cheap. Of course, it's not still free. And in order to get it to become free, we need to discover a room temperature superconductor.

And there's some very exciting research going on at the moment where basically materials containing hydrogen, which is of course the lightest element, are being squeezed to phenomenal pressures. And inside that chamber, they're getting superconductivity, getting very close to room temperature. Do you want to take that on? Yes. So I think the problem, of course, with those superconductors is that they require pressure. of about 2 million times atmospheric pressure. So that's not going to be useful.

But I think the exciting thing is that we have this sense that out there in the large space of different possible chemicals that you can discover, there are going to be new superconductors. And this goes right back to what Citra was saying earlier on about emergence. So the idea of emergence actually comes from the 19th century, John Stuart Mill, in his system of logic. He had this idea that if you take something like water H2O, water is not like hydrogen, it's not like oxygen.

Those are colourless odourless gases and water has this quality of wetness. So how have you taken these two completely different things together and made something utterly new? And similarly, if you take an alloy, you take two completely different metals and you end up with something that has completely new properties. Now if you start making compounds with not just two elements in them,

but three or four, the number of possible emergent behaviour just boggles the mind. And I think this is what gives all of us great hope because even though we haven't found a room temperature superconductor yet, we see discoveries being made all the time, we're part of those discoveries,

and we have this sense that there are materials out there that we can find. So what are we going to do when this revolution happens then? Do we take for the hills or do we embrace it? I think the revolution is happening, I think, where we're living through it. And I think, yeah, superconductivity, just one of the incredible phenomena that is changing our lives.

But yeah, I think there's many more fundamental emergent phenomena that will similarly translate into applications. Do you think this is going to make a new world? I think it is going to make a new world. It's crept on us slowly. 1911 is a while ago. But the exciting thing, I think, when you look at the history of superconductivity is every decade there's a huge breakthrough which changes our views.

and it usually comes in an unexpected way. And so I think that's very likely to continue. I think even though Faraday, of course, was a century before the century of superconductivity, I think he would be very pleased that it does seem to come down to this interaction between electricity and magnetism, which all his experiments were about. We're looking for a new world with you three, leading us into a new world. You're nodding very vigorously. I love that idea. Why else would you do physics?

Thank you all very much. I'm sure people love that. Thank you. Thank you, Nigel Hussie. Sushita Sebastian, Stephen Bundell, and our studio engineer Steve Greenwood. Next week, the 16th century Danish astronomer Tycho Brahe, renowned for his accurate observations of the heavens in a world without telescopes. How about that? Thanks for listening. And the In Our Time podcast gets some extra time now with a few minutes of bonus material from Melvin and his guests. What would you like to have said that you didn't say? Who wants to start, Stephen? I think one historical aspect that I think doesn't get a lot of press, but we could have mentioned, is when the Meissner and Ostenfeld experiment was done in 1931,

they had some competition. And Lev Shubnikov was working in the Ukrainian Institute in Kharkiv. And his story is rather interesting. He was born in St. Petersburg. went to the Camerling on this laboratory in Leiden and learnt his craft. He invented an effect called the Shubnikov-Dehase effect, which I think all three of us around the table have worked on, used it as a technique for studying the resistance of materials.

And then when he went to Kharkiv, he set up a group using low-temperature physics. And in 1931, he also discovered the Meissen effect. But unfortunately, the great Soviet physicist Landau told him it was rubbish, so he didn't publish. so he didn't publish. And so he only published a year later and he'd been pipped to the post by Master and Offsenfeld.

Russia came down there. That's right. He then went on to do some important work in understanding these type two superconductors that Nigel talked about. And in 1937, he was called into the lab one evening and left his dinner at home and he was never seen of again.

He was taken away. His wife was eventually told that he died of a heart attack in a Soviet prison in 1945, but in 1991, the NKVD archives were opened up, and he'd actually been shot in 1937 a few months afterwards. Essentially, he'd fallen out with the local party officials, and it was the time of the Great Purge, Stalin's Great Purge, and he was just a victim, and you think what he would have done had he lived. So I think... What was he doing? It made him want to shoot him?

It was nothing, really. It was a petty falling out. with local officials, but there was murder in the air, and so so many people perished at that time. Wasn't Landau himself also arrested? Landau was also arrested. But thankfully not executed. But not executed, that's right. I think that also tells us a little bit about,

yeah, the problem with there being too much influence from people who think they know. So Landau telling this young physicist it was impossible, and I think probably all of us have been told at some point. point in time something we've been working on or found is impossible and it couldn't be. And I remember these moments where you'll give a talk at a conference and someone will stand up and say, this is impossible and declare to the room why it's impossible. But I think what I really love, especially about being experimentalist, and I think there's a couple of things. I think one, I think it's great that we actually do have the space to keep going.

despite not having consensus and the possibility to not go along with the party line and say, actually, we don't know that it's impossible just because you think it is. That is what nature tells us. And I think that it is one of the reasons that we make progress is, despite being told something's impossible, you keep going and discover a new feeling. phenomenon and that I think is one of the things I love about doing physics. I mean, as experimentalist, I think we are all experimental. So, you know, I think, you know, the challenge of trying to understand high-temptry super connectivity,

again, people say, well, it's decades old. Why don't you just stop and go and do something else? And, you know, it is one of the biggest challenges of modern times for, you know, in terms of physics. And I find it's remarkable, actually, that something like 15 Nobel laureates have written articles on high-term superconductivity. I, for one, know of no other subfield in physics that has energized or sparked the imagination of so many of the greatest minds.

But, of course, we haven't been idle. You know, all the time we've been trying to understand the physics through experiment. We've been developing those experiments. I think one of the great legacies of research into this superconduct, this new generation of superconductors is what it's done to all our techniques, you know, expanded them, taking them to new energy regimes, new degrees of resolution

that we could only have dreamed about 20, 30 years ago. And so if we never solved the mystery, we've left behind this great body of, you know, very sophisticated experimentation that we can now apply to any material and any new emergent phenomena. And I think then, you know, we just need that new generation of smart people to come along and crack the code with these techniques. How would you encapsulate the mystery? Well, yeah, I mean, I think one issue is that lots of problems in physics are solved by breaking everything up into the smallest components. That's the standard physics way of doing things.

You smash something into the tiniest pieces and study the elemental pieces. And this is a problem where you can't do that, as we've all been explaining. It's where electrons are not acting as individuals, but they're actually acting together, either in pairs or actually a condensate of pairs. Probably entangled. Entangled, quantum mechanically entangled, pears. and this condensate, this grouping of, as Situja was saying, 10 to the 23 of these things in a macroscopic sample. So you can no longer use that kind of thinking where you smash things to bits and try and understand the bits. You have to think in new ways. And I think that's why it's

turned out to be such a challenging problem, but also such a fascinating problem. Yeah, I think in terms of emergent phenomena, I think Nigel was saying, you know, we've run out of sort of theories to explain what's happening with current theoretical machinery. But I think as Stephen was saying, yeah, I think we might be sort of on the front of having to enter a new theoretical paradigm, as it were. Like a new language. Yeah, a new language of working in terms of emergent phenomena, because I think think we're all so used in the field of physics to having models that reduce things down.

So we start with these building blocks, build them up, and assume that the fundamental is that smallest building block. But now we have emergent phenomena which can't be reduced. And it is really exciting, actually, to think that if theories are failing, then it's maybe not a failing, but more something that's telling us that we need to think completely differently. and think of emergent theories that start with the fundamental as being the macroscopic and not with the fundamental as being this tiny particle that is being built up. And I think there's so many of these magical, unexplainable emergent phenomena that we know of. And they've all sort of been put to the side because we don't know how to explain them.

But I think maybe this is just pointing to theories that are emergent, a new language has to be developed to begin to describe them, to be able to converse about them in a way that isn't just unexplainable. You're hovering at the door. Okay. And we'll have a message for all of us. Cheer or coffee. Perhaps you've got more to say.

I think Nigel was... No, I would like some tea. That's what I would like to say. Yes, please. Tea, tea. in our time with Melvin Bragg is produced by Simon Tillotson. My name is Jonathan Meyerson, and two years ago we produced Nuremberg, a dramatized reconstruction of the trial of the major Nazi war criminals.

Their crimes were indisputable, but one mystery remained. How did this group of unremarkable men come to rule all of Germany? Our new podcast, Nazis, the Road to Power, unravels this improbable story in 16 episodes starring Tom Mothersdale, Derek Jacoby, Alexander Vlahos, Toby Stevens and Laura Donnelly. It remains a lesson for us all. Listen wherever you get your podcasts.