Daniel and Jorge Explain the UniverseCan something be both a conductor and insulator?
Daniel and Jorge talk about the recent revolution in solid state physics that has led to weird new materials.
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Hey Daniel, I've got a really easy question for you.
Oh, those are the trickiest ones.
I relaxed. I'm sure it'll be trivial, but here we go. What is a medal?
Uh? Oh? Kind of depends on what temperature. Actually, it depends on whether you're an astronomer, a geophysicist, or a solid state physicist.
But those are all physicists. You can't agree on what a medal is.
No astronomers think that anything heavier than helium is a metal, and a solid state physicist thinks that anything that conducts electricity is a metal.
Mm sounds like a little disaster.
Don't get me started on how we define heavy metal?
Why? Because you have to call the music physicists.
It depends on the number of electric guitars involved.
And how do you define space elevator music? Who do you call that?
Hi?
I am Horehem, a cartoonist and the creator of PhD Comics.
Hi, I'm Daniel. I'm a particle physicist and a professor at uc Irvine. And while I do want to ride in this space elevator, I've given no thought to what kind of music I want to hear as I'm riding up into space.
M I guess you want maybe cosmologically classical music.
Maybe maybe I want the opening music to our podcast, which is sort of spacey.
Want electric music because you know that's a physical property.
Yeah, I definitely don't want anything catastrophic.
Or electromagnetic orchestra emo music. But anyways, welcome to a podcast. Daniel and Jorge Explain the Universe, a production of iHeartRadio.
We are your mental musical accompaniment to our ride through the universe, elevating ourselves up into understanding the very nature of space and time and fields and particles. We go up and down while we examine what we do know and what we don't know about some of the deepest questions in the universe. Where did the universe come from? How is it gon end? What does it all mean? Anyway? We talk about all of these things on the podcast, and we try to explain as much as we understand to you.
Yeah, because it is a pretty musical universe. It sounds a little melodious and sometimes kind of chaotic and definitely epic. It definitely has an epic score of quality to the universe.
That's right, And definitely kudos to the audio engineers for the universe. There's so many really cool sound there. If you just sit out there and listen, you hear all sorts of squishing and banging and squeaking, and wow, the universe is definitely chock full of cool special effects.
Yeah, and we listen to the universe in all kinds of ways, right, Like there's sound waves, there's electromagnetic waves, there are gravitational waves. It's like the universe is a symphony using all kinds of instruments.
You think any collection of sounds is a symphony. Like when you pick up your kids from daycare when they're two, you consider that sound a symphony ten screaming children.
Depends on my mood. I guess, am I feeling like a cacophony of two year olds? Or would some peace and quiet be nice as a parent?
Sort of like early heavy metal, all they're doing is shouting.
Anyway, one person's music is another person's heavy metal screaming.
But it's true that the universe is filled with incredible and amazing things. And as we look around, we're continually impressed by the complexity of stuff that we see around us. You know, it's not just one kind of sound or one kind of object or one kind of material we find out there in the universe. There's all sorts and enormous variety and complexity of things that we get to dig into and try to understand.
Yeah, because I guess even after millions of years of being humans and looking at the world and listening to the world, there are still things about it that surprises, Like we are still finding out new kinds of materials and new ways in which matter behaves.
That's right, because it turns out that the things around us are not the basic building blocks of the universe. It's not like there's a fundamental ice cream particle and a fundamental tuna sandwich particle that makes that the things you eat or the things that are you. Everything around us is actually made of really small little particles arranged in different ways, and those arrangements can do startling things. You take us out of particles and you can make a kitten. Rearrange those same particles, and you can make lava or neutron star or a blueberry sandwich. It's all the same bits, just arranged in different ways, and we're continuing to discover other ways to arrange those bits to make new, even weirder kinds of stuff. Yeah.
Wait, are you telling me that ice cream is not a fundamental article in the universe. It should be.
I mean, I know, it seems like fundamental to our existence in it's hard to imagine being human without ice cream. But you know, most humans who have ever lived never had ice.
Cream, and that is called the human tragedy in literature.
Think about it this way. That means there might be some dessert invented by future humans that you never taste that future humans can't imagine life without.
I find it hard to believe that they can improve on ice cream. I take hope in the fact that in the long run there will probably be more humans that have eaten ice cream than them have not.
Well, that's an optimistic view, but I think ice cream is a great example because it's obvious to us that ice cream is not fundamental to the universe, right like ice cream takes special conditions in order to exist, and nobody would be surprised to learn that there might have been a time in the universe when there was no ice cream. It's the same kind of question we ask about other things about whether they're fundamental. Is it necessary to have electrons in the universe? Are they fundamental? Or could there have been a time before there was a life electrons? Could there be a time in the future without electrons. That's sort of the question about whether something is fundamental or whether it emerges from the complex interplay of fundamental things.
So more humans used electrons than not used electrons.
Humans are made partially out of electrons, So I guess we've used them in everything we do.
Right, Well, I look forward to our future episode about the physics of ice cream. But today on a podcast, we'll be asking a different question about matter and the different ways that it can come together and do interesting and new things. So our question for today is what is topological matter? Topological matter? Huh? That's not an everyday word.
It's not an everyday word. It's a very recent discovery. Physicists working in their basements with their lasers and their super cold temperatures and their bizarre materials, have been able to concoct kinds of things no human has ever seen before. To put these same ingredients together in new recipes to make weird, new kinds of matter that can do things that our familiar matter just cannot do.
Man, physicists. First, we're talking about physicists as musicians. Now we're talking about them as cooks or mad scientists. I wasn't quite sure what you were going for there.
I think there's a big overlop between cooks and mad scientists bakers. I think a big part of being a baker is being a mad scientist. You know, like what happens if I just put a lot of butter in this recipe? Let's see.
I don't think that's what I want to hear from when I go to a restaurant. It's like the mad scientist today has a very special treat for you.
That's how all of French cooking was invented. Let's just add more butter and see what happens.
Oh, man, you just call it all of French culture.
Man, No, there's an insanity to their creativity which has led to this exquisite discovery of their pastries.
They're creative. Yes, yes, that's what we call those kids in class, that kids really creative.
I'm looking forward to when the French invent the topological pastry.
How do you know they haven't?
Can you deform a crossand so that it's equivalent to another pastry?
What is the shape of a cro really? And is it a croisson if it's not that shape?
Yeah? Well, you know, sometimes we ask if the universe is actually the shape of a donut, but maybe we should be asking if it's the shape of a croissant.
Right, And each quantum field is like a layer in the flakiness of the croissant.
That's right, Quantum lemonation theory.
Quantum croissant, quantum heart attack? Really, what is what we should call it?
For all the ridiculous quantum things out there? I don't know if anybody's ever done quantum.
Pastry yet, I mean rich idea.
Yeah, but you know, every time I say that on the podcast, we get an email from a listener who's like, actually, here's an example. They sell this around the corner. So, folks out there, if you've eaten a quantum pastry, send me the recipe.
Actually, here's a season desist letter. Stop talking about my product. But yeah, topological matter. That's a pretty interesting idea for a name for a kind of material. And I imagine I mean the word topological comes up a lot in like map makers, right, and I guess architects and you know people build houses, they have to deal with topological maps a lot, right, Exactly.
The yield of topology is the one that studies questions about shapes and surfaces and asks questions like can you take a donut and smoothly deform it so that it turns into a coffee cup, for example, And the answer is yes, you can. So a topologist says that like a coffee cup and a donut are basically the same shape, and they're both different from like a sphere because the sphere has no holes in it, and a donut and a coffee cup both have one hole in it. So that's the field of topology interesting.
And so if you take a donut and dip it into a coffee cup, what does that give you?
It gives you a soggy donut.
Is that a new kind of shape is the same as a sphere? If it sogs, doesn't it become a sphere?
It requires an entirely new field of math. Soggy topology hasn't been invented yet.
Deep questions here today and new fields being invented around every corner. But yeah, it's kind of an interesting question. What is topological matter? Maybe it's not something people have heard, or maybe it is something people have heard. So, as usual, Daniel went out there to ask people on internet this question.
So be grateful to these volunteers who were willing to answer a random question without preparation and have their voice played on the podcast. If you'd like to play along for a future episode, please, I totally encourage you. Right to me two questions at Danielandhorge dot com.
Think about it for a second. How would you answer the question what is topological matter? Here's what people had to say.
So I hear the word topological, and I think of a topological map, which sort of gives you an idea for how things are spaced out and organized the elevations. So I'm wondering if topological matter has to do with like the number of protons and neutrons and a nucleus or something.
I don't know.
I think topology is the study of two day and three day shipes and their properties, and I think there's some rules about how you can compare different shypes topologically. So my guess is the topological map is matter that conforms to the rules of topology.
Topological matter I haven't heard of before, but I imagine it's matter with measurable geometry to it, existing in three D space instead of a point matter, which might be black hole.
I have never heard the term topological matter before, but I think topological is some geometry which has fixed properties. So maybe topological matter is matter whose properties does not change. But I don't know which property is.
I'm guessing it's when we're talking about matter and topological I'm guessing it's the shape of sub atomic particles.
I have no idea what topological matter is. Is it something that you make maps out of? Topological topography? Math is map making, right, I don't know.
Topological matter is all of the matter we can see in a three D you know?
All right? Pretty interesting questions to feel like there's a deep level of knowledge about physics here because I hear a lot of words related to physics.
Yeah, people definitely get the clue also that it's related to topology and geometry and thinking about shapes and structures and maps.
I like the person who said it's all the matter in the universe technically, yeah, I mean in the universe, there's all kinds of matter.
Hmmm. Yeah, that's true. It's something in the universe. That's a good answer to the generic physics question.
But do you say something in a universe or the.
Universe or in our universe?
All right, So it's a kind of an interesting question let's dig into and this conversation is going to get pretty mind blowing and pretty technical and detailed here. So let's start with the basic question, Daniel, what is topological matter?
Yeah, topological matter is something we've only recently invented in the last twenty years or so, and it's something that's different from anything we've ever seen before because it's neither an in something that cannot conduct electricity, nor a metal something that can conduct the electricity. So solid state physicists used to divide all kinds of stuff into two categories, insulator or metal, and now they've developed this thing which is sort of like neither and both.
Mmmm.
I see. So solid state physicists is like a physicist that studies I guess solid things. Like they don't study energy or particles, they study like materials.
Yeah, exactly. Sometimes they're called condensed matter physicists, and you know, they deal with things like in a lattice, like a crystal, like a big blob of stuff, not plasma, not liquid, but like just a blob of stuff. And the name of the game there is like can you rearrange stuff so it has weird properties? Because you know, I as a particle physicist, I study like one proton at a time or two of them smashing into each other. But we know that when these protons get together with electrons and make all sorts of interesting structures, crazy things happen. You can get carbon, you can get diamond, you can get all sorts of bizarre stuff. You get ice cream, proissants. Yes, yeah, it's sort of a study for like how properties of materials emerge from rearranging the little bits inside matter into new arrangements.
Right, And it's like solid stuff. It's not stuff that's like flying around or you know, moving or it's like what can you do with this solid thing?
Exactly? And the question of you know, what's a metal what's a conductor is very important because some of this stuff goes into fueling lack our electronics industry. You know, we need insulators and we need conductors to make circuits, and so you can make like new kinds of stuff that has interesting properties. You might be able to make like new weird electronic do higgys that power the next generation of quantum computers that you use in your phone as you ride the space elevator up to the moon.
Yeah, listening to space elevator music on your a quantum phone. And so you're saying that they see the world as or they see materials usually as either insulators or conductors.
That's right. The whole theory of condensed matter physics until about twenty years ago was that materials are either insulators or metals, and they have this whole theory about electrons in bands inside the material that help them understand that.
Okay, so let's get into how do you define conductivity and what makes something not conductive or an insulator.
So it's easiest to start out with an individual atom. You remember that an atom has a nucleus of right at the core where you got protons and neutrons. That's where most of the stuff is of the atom. And then around it are the electrons, and electrons around an atom have these energy levels, right because they're quantum particles. But now we want to think about a whole bunch of atoms, right, you want to put them together, stack them together like legos to make a blob of stuff. Because that's what condensed matter, solid state physics is about, is about like a crystal, a lattice of stuff. So material is sort of like a grid of atoms. And now we want to think about like how electrons can move through that grid of atoms. And you know, an individual atom has its electrons and the next one has its electrons, and the material is a conductor when an electron can hop from one atom to the next, when it can sort of like jump around, slide around easily. And material is an insulator when it can't, when it's sort of like stuck on one atom no matter how hard you push it.
Well, I think this is something that maybe a lot of people don't think about when you know, I think when you grow up and you learn about like a wire conducting electricity, you think of like one electron going into the wire and then traveling through the wire and then coming out the other end. But really that's not what's happening in conducting metals. It's more like electrons are being passed, traded around from one end to the other.
Right, that's right. You should sort of think of it like a hose, but instead of an empty hose that you're passing one electron all the way through, think of it like a hose that's already filled with electrons. You're pushing one in and then another electron pops out the other side. So all the electrons slide down the hole like one notch, and one electron pops out the other side, but not the one that you put in originally, you know, on.
Your side or maybe right, like, we don't know. It's a bit of a mess. It's like you put an electron on one end and maybe that one will hop to the neck one, or maybe we'll stay, but it'll kick off an electron from the existing atom, and that one will go to the next atom, and who knows what's going to happen, right.
Yeah, Well, the more orderly it is, the more it happens, like you know, everybody's sliding down one chair in the bus or something, then the better the conductivity. The more messy it is, the more electrons bounce around and go in the wrong direction, the worse the conductivity is. That's why we have some conductors that are excellent in some conductors that are sort of poor conductors.
Right, And so what makes something more conductive or one atom more prone to conductivity than others. Is it just that it's electrons aren't like held on tightly, or that they're at the surface and you know, the atom can sort of take them or leave them.
The key thing is what energy levels are available to the electron. So for an atom, you just have like a ladder of energy levels, and the electron can go up or down those energy levels. But when you put all these atoms together to make a material, something different happens. Instead of having just like a full ladder of energy levels, you get these bands that the electron can be in. So you have like a bunch of energy levels clustered together, and then a gap where like electrons are not allowed to have those energies, and then maybe there's another band above it. And so this makes something an insulator if, for example, a band is all full. If a band is all filled with electrons, the's like no room for electrons to jump in there unless they have crazy high energy. So an insulator is one where you would need to give the electron enormous energy so it could jump up into the next band to move around, but normally electrons don't have that energy, so they're sort of stuck where they are.
I feel like we're talking about heavy metals and bands here, and it's confusing my brain a little bit. I think what you mean is, you know, electrons are happy in certain energy levels around an atom, but when you put a lot of atoms together, you know, things get kind of fuzzy now, and an electron can be happy sort of at multiple levels because it's near another atom, right, But sometimes it can work out that there are big gaps in like these energy levels. That's what you mean by a band, right, It's like a sort of like a gap in the sort of the different levels that's right.
The band are the allowed energy levels, and then there's gaps between these bands, and insulator has a really big gap between the bands, and the lower band is like all filled up, so that if an electron is in that lower band, it can't just like jump to the next atom because the next atom is also filled up. There's like no empty chairs in a conductor. In a metal, then the band is only half filled, and so the neighboring atoms have empty chairs for an electron to jump into they can slide over to the next one, sort of like if you have a bottle and it's half filled with water, it's a lot easier to slash the water around than if you have a bottle it's totally filled with water, because it's sort of like packed in there. Nothing can move. And so if you have your band half filled, then the electrons can slide around from atom to atom. If your band is totally filled, that's an insulator, then the electrons are sort of all stuck and nobody can go anywhere.
Right, But I guess you make it sound like it's just a matter of having too many or too little electrons it's really, But really it's more of a question of like the structure of the crystal.
Right exactly. These bands come from the structure of the crystal. Like you might wonder, why are there bands in a crystal when there aren't bands for an atom, There aren't like these gaps where electrons are not allowed to have the energy level in an atom. Where do they come from in a crystal? And that's the really interesting thing, right When you put atoms together into a crystal, they get properties that the individual atoms don't have, and what's going on is the spacing between the atoms. As an electron passes through the crystal, sometimes it reflects off of those atoms and bounces back and diffracts and destructively interferes with itself. And so if the energy of the electron is such that the wavelength of its wave function is similar to the spacing of the atoms in this crystal, then you get all sorts of complex destructive interference, and electrons basically just can't have those energy levels.
M interesting. It has to do with the waveform of the electrons and how close or how far apart the crystal puts the atoms together exactly.
And the really fascinating thing is that you could take the same material, the same elements, and arrange them in different crystal structures and you get different bands. So, for example, if you take ten tin has two different cris structures, they call it gray tin and white tin based on how it looks to your eye, and white tin is a conductor, whereas gray tin is an insulator. It's exactly the same stuff, but you can build it together in different ways, sort of like using the same legos to make something slightly different. The crystal relationships are different, and so the spacing is different, and so electrons behave differently in those materials.
Because I guess, you know, the properties are the levels of one atom sort of start to interfere with the properties and levels of its neighbors, and so things suddenly become like prohibitive or easy to kind of move around, exactly, And.
The properties of a whole set of things can be very different from the properties of one. Like you ever go listen to, you know, children's choirs, like, well, one kid on their own kind of terrible, but if you get like thirty kids singing a song together, like it sort of averages out to give you, like something maybe pleasant to listen to, spoken like a true parent exactly. And so I think this is really fascinating. And for a long time and people thought, well that was it. That it's all about having these bands and it's determined by the crystal structure, that the crystal structure tells you whether something is insulator or something as a conductor. And this is called the band theory, and it's sort of rained in condensed matter physics for decades and decades, and people thought this is how conduction works in materials.
M It's all about the structure of the crystal. Like at the arrangement of the atoms, that will determine what's an insulator or a.
Conductor exactly, and like not the shape of the material. It doesn't matter how big a blob you have, or how thin it is or how thick it is. It's just about the nature of the material and its crystal structure.
This reigned supreme. People thought of this for a long time. But I'm guessing that there's a twist to this story where everything is proven wrong. That's usually how it works in physics, isn't it.
That's right. Here comes the revolution and.
So let's get into the plot twist here. But first let's take a quick break.
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All right, we're talking about topological matter, and we were talking about how we used to think that everything was either a conductor or an insulator, meaning it can conduct electricity or not conduct electricity, and that we thought it had everything to do with the way that the structure of the material in the way in which the atoms sort of compacted together and form crystals. But now there's a plot twist, Daniel, So we'd learned some new information.
That's right. Clever people thinking hard about the way these things work came up with an idea for how to build a new kind of material. And this is super cool because it came out of people's brains. It's not something we discovered in the lab and we're like, look at this weird kind of stuff we build. Oh my gosh, you can do something weird. This came out of smart people scratching their heads and drinking coffee and scrillling in their notebooks and doing calculations, and they were able to come up with an idea for how to build something which is called a topological material, which is an insulator on the inside, but a conductor on the surface. So like the outer edges of a blob of this stuff will conduct electricity, but the interior of it will not.
Hmmm.
Interesting, So sort of like a coating almost, Like you have something that doesn't conduct electricity, like a ceramic or something, and then you cod it with something that does conduct electricity.
No, it's all one material. So you have like some kind of material and inside it doesn't conduct electricity, but then the same material on the surface. The surface of that same material uniform and homogeneous what the stuff is, but the surface of it does conduct electricity.
Oh wait, it's the same material with the same structure, or is it on the surface you have a different structure.
It's the same material with the same structure. But now the behavior of the material depends on where you are in the shape. If you're on the edge, you conduct electricity, if you're in the middle, in the bulk, you insulate.
WHOA, So how does that work? Like how can something conduct only on the surface.
Yeah, it's really interesting. It has to do with how electrons move. And so we talked previously about insulators being when electrons are stuck. So now imagine a material where electrons aren't quite stuck. They're not like exactly stuck on one atom. They can sort of like move in little circles. And that doesn't allow this to conduct electricity because electrons like sort of can't move all together. Like you move in a circle, you end up back where you started, so there's no effective flow of electricity. But if electrons are moving in a circle, then think about what happens on the surface or near the surface. Instead of having electrons move in little loops, their loops are sort of like cut in half, and so now they can only do sort of like half of the loop before they hit the surface, and then they can do the next loop, and the next loop in the next loop, and that sort of like adds up. So the electrons can now flow all the way around the edge of the material because they're only doing half of these loops.
Wait what, well, I guess first of all, back up a little bit. What do you mean electrons move in little loops, like little loops around the atom, or little loops like around multiple atoms, or what do you mean? Because they're already sort of in loops in orbit around the nucleus of each atom. So what do you mean by they move in loops.
The first idea for how to build these things was to have them move in little orbits around several atoms. And they created this first by having really powerful magnetic fields which will make electrons move in little circles.
Why do they think to make electrons move in circles.
Because they were hoping to get exactly this effect. They were hoping to do something which on the center of the materials would make us so the electrons effectively can't go anywhere because they're stuck in this circle, but that on the edges would have a different behavior that you know, these circles are sort of cut in half on the edges, and so they only go in one direction. Like in the center of the material, the electrons basically go back and forth because they're moving in a circle, but near the edges they can only do the back right. So all those electrons are now moving in the same direction, and that's effectively conducting electricity. It's like having a flow of the electrons all the way around the edge.
Okay, so you need an electromagnetic field to make these things go in little loops or were you saying that these things go in loops anyways.
So the original design for these things, and the first way they were realized in the lab, was to make a really strong magnetic feel to make electrons do this. Later on people realized, oh, there are other ways to do this, you know, just to get the electrons to like do loops around their atoms and to couple like their orbits and their spins. But that's a bit more technical. So the first way people made this happen was to have the electrons do these little dances in a circle. It's sort of like a big square dance, right. Imagine everybody's like dancing and they've hooked their arms together. You're not really going anywhere, but if you're on the edge, then you're sort of getting passed from partner to partner and you're going to end up moving all the way around the square dance.
So wait, you're saying that. Normally the electrons don't conduct, but they move in circles around inside of the material. So it's a conductor on the inside, or no.
It's an insulator on the inside. Because electrons are trapped, they can't really go anywhere. They're stuck moving in these circles. But it's a conductor on the surface because these circles are cut in half, and so the effective path of the electron is all to point in the same direction.
Oh, I see, Okay. I think asking us to sort of think about these loops and these structures is kind of hard on an audio podcast, But I think what I'm getting is that inside of the material, the conditions of the crystal are such the electrons that are sort of stuck moving around in circles but at the edge is because there's no full circle they can do. Then they can then jump around and move to other atoms. Is that what you're saying.
Yeah, they can jump from atom to atom on the surface exactly.
Because you're sort of breaking the conditions that are making them be stuck in these loops.
Yeah, they only do half of the loops, right, and the half of the loops basically always point in the same direction. So you do half of one loop, then you do half the next loop, and half the next loop. You never do the other half of any of these loops because the surface is there sort of preventing you. Let me just try one more visual analogy. So think about like a swimming pool in your backyard. Now put a lot of tiny whirl pools in it, all swirling around. Fill the whole thing up with whirlpools. Now what happens if you toss a ping punk ball into it, Well, it's going to get stuck in one of the whirlpools and it'll be really hard for it to jump from one to the other. So that's like an electron getting stuck moving in a circle around one of the atoms in a crystal. But if you put it right at the edge of the pool where the whirlpools are all pushing in the same direction, so that instead of getting stuck in one whirlpool, it moves around the whole edge of the pool, getting passed from one whirlpool to another. So it doesn't conduct electricity in the center, but it does around the edges.
So that gives you a material if you can make it, that doesn't conduct electrons through the material, but it conducts electrons on the surface of it.
That's right exactly. And this sort of blew everybody's minds because they were like, what is it. Is it an insulator, is it a conductor, is it both? Is it neither? It's something new, And so this sort of blew up this whole band theory of materials and made people realize that there's like a whole possibility for new things that you could build that have weird behaviors that you didn't possibly anticipate. And the cool thing is that this idea came about and just like a couple of years later, people were able to make them. So went from like crazy idea in somebody's notebook to like, Okay, we made it, we saw it actually do this thing in just a couple of years, which is sort of astounding.
I guess maybe the confusing thing might be that the way you describe it doesn't sound so different, Like what I could just maybe take a ceramic and code it with conducting metal and I would get something that's conductive on the outside and not on the inside. Like, why can you explain maybe why this was so revolutionary.
Well, it's different from having a ceramic coded with a metal, right, that's just having a metal that conducts. Here we have something which is fundamentally different because it's the same material all the way through, but the material behaves differently on the inside and the outside. And it's exciting because it suggests that you can get new properties for familiar materials, the materials you thought you knew, you might get them to do different kinds of things, different weird kinds of things if you create new conditions for them, that there's like a whole other avenue. It's sort of like you've been playing with your legos for ten years and then your friend comes over and builds something mind blowing and you're like, what I never thought legos could do that. That's awesome, and it gives you ideas for all sorts of other things you might be able to build with your legos you never even considered. And in this case, it's exciting because the outside surface of these topological conductors are very very low resistance. For example, they can conduct electricity better than copper, better than gold. They're not quite superconductors with zero resistance, but they're better conductors than almost any material we have, and they operator room temperature. So it's promising that there might be like new kinds of things we can build.
And that's kind of what it's called topological matter because it sort of happens on the surface, like the fun things happen on the surface.
It's tempting to think about that because it sounds like we're saying, well, the properties of these material doesn't just depend on the crystal structure, you know, on like the organization internally, but also in the shape of the object, because originally these things were made super flat, and we're talking about like the shape and the structure of it. Actually, in this case, topological refers to something much more technical. Physicists like to think about these things in terms not in physical space, but in something else called momentum space, where you do like a four y transform from physical space to momentum space, and then in that momentum space they're doing some complex analysis, some complicated counting of the shape of that space, and it turns out there are really interesting symmetries there, like states there that have the same topology will tend to have the same kind of behavior, will be an insulator or will be a conductor. But I think that's a little bit deeper on the maps that we want to get into today.
Well, I guess maybe step us through then what are some of the ways in which it blew people's mind, Like, what were some of the cool things that people found you can do with these.
Well, we're just really beginning in exploring what you can do them. And we're talking a minute about potential applications. But one of the really interesting things is that people went back to old experiments that they never really understood before. Like people have been, you know, doing weird things with gold for a long time, and sometimes they would do experiments and not really understand the results and see they were sort of scratch their head and then move on. And now with this new understanding, we can look back and realize, oh, we were seeing topological effects in ordinary materials. We just didn't really understand it. Like people took gold and they made like thinner and thinner sheets of gold, and they studied the conductivity of it, and they were sort of surprised that it didn't really depend on like the thickness of the gold and only depended on like the surface area of the gold. And that was weird because people thought, like, hm, it should depend on you know, the crystal structure and what's going on inside. And so there's like a whole list of experiments that people didn't really understand that sort of befuddled the field. And now people go back and like, oh, wow, it turns out that's a topological material and more broadly as we look at it. Now people are realizing that something like one third of all materials that are out there have some sort of these topological effects that it turns out to have been everywhere all the time, we just never noticed it.
And the other two thirds just don't have these effects mm hmmm.
And so now we're doing these like really complicated calculations to try to understand, like under what conditions can you get these kinds of effects. And it turns out that, you know, a lot of things that we think of as insulators turn out to have some amount of topological conductivity, and things that we think about as conductors sometimes are insulators on the inside. And so it's like being unaware of a third phase of matter.
You know.
It's like if you're a fish scientist, you've been swimming around water forever and then you go to the surface and you discover, oh, wow, there's other things. You know, water has other phases I never even realized.
You know.
It's like opening up an entirely new area for people to explore. It's really the beginning of a revolution in condensed matter physics.
It's like maybe like figuring out that water can form little layers on solid things, and then little animals can live on that surface. Stuff like that.
Yeah, or like a fish discovering rain, You're like, oh wow, water falls through the sky and these weird little drops. How interesting.
I invented an umbrella exactly.
And the other interesting thing is that this is a discovery that was just sort of like sitting there waiting to happen. Like the mathematical tools that were used to come up with this idea and then mid two thousands are ancient. This could have been thought of in the fifties, and the experimental results were sitting out there in the literature for decades. You know. It's like this pattern of unexplained experimental measurements that nobody was able to put together. So when they put this story together, it's sort of like, oh my god, it's so fascinating but kind of obvious. And that's really exciting to me as a physicist because it tells me, like, well, what other discoveries are just out there waiting, Like there's gonna be a whole series of Nobel Prizes, one for topological material and all of that information was just like literally sitting out there waiting for almost anybody to put it together.
Now is a Nobel Price metal going to be a topological material as well?
Well.
One cool effect I think you wrote down here is that you can take an insulator and turn it into a conductor and back again just by changing its shape.
Yeah, people used to think that if you had a material that's an insulator and you sort of started pulling it apart, you made the atoms further and further apart, then it would stay an insulator because as the atoms get further and further apart, obviously it gets harder and harder for electrons to jump from one to the other. And so this is sort of like a common belief that all insulators are insulators even if you pull them apart. Well, if you have a topological material, then what happens when you start pulling it apart is that that insulator at the core becomes a conductor because you're effectively now creating like new surfaces, and these things can conduct at surfaces. And then as you keep pulling it apart, then you know, the atoms get so far apart that they're basically not part of a material anymore, and it's effectively an insulator. So it's a really weird kind of material that you know, the conductivity of it also depends sort of on how you smoothly deform it.
Interesting, So it didn't conduct before, even at the surface, but once you pull it apart, you're sort of rearranging the atoms in such a way that suddenly on the surface it can conduct.
Yeah, exactly. It's really interesting. And so this gets condensed matter physicists very excited about the kinds of things they might be able to invent using these techniques or other techniques similar in the future.
Are they thinking topological ice cream?
That's right, it's frozen in the middle and liquid on the center.
I mean that discovery has been there all these years for people to find.
That's right. You get the ice cream Nobel Prize, the Nobel Prize made out of ice cream.
Yeah, you just have to keep it in the freezer otherwise it melts. All right, Well, let's get into what this new kind of material can do. What are some of the exciting things that might be able to be made from these and what the potential of that is. But first, let's take another quick break.
When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt. You're probably not thinking about the environmental impact of each and every bite, but the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US Dairy tackling greenhouse gases. Many farms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit usdairy dot com slash sustainability to learn more.
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Hi.
I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I'm a neuroscientists at Stanford and I've spent my career exploring the three pound universe.
In our heads.
We're looking at a whole new series of episodes this season to understand why and how our lives look the way they do. Why does your memory drift so much. Why is it so hard to keep a secret, When should you not trust your intuition? Why do brains so easily fall for magic tricks? And why do they love conspiracy theories. I'm hitting these questions and hundreds more because the more we know about what's running under the hood, the better we can steer our lives.
Join me weekly to explore the relationship.
Between your brain and your life by digging into unexpected questions. Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts or wherever you get your podcasts.
Hi everyone, it's me Katie Kuric. If you follow me on social media, you know I love to cook, or at least try, especially alongside some of my favorite chefs and foodies like Benny Blanco, Jake Cohen, Lighty Hoyke, Alison Roman, and of course Ina Garten and Martha Stewart. So I started a free newsletter called Good Tastes that comes out every Thursday, and it's serving up recipes that will make your mouth water. Think a candied bacon, bloody mary tacos with cabbage slaw, curry cauliflower with almonds and mint, and cherry slab pie with vanilla ice cream to top it all off. I mean, young, I'm getting hungry. But if you're not sold yet, we also have kitchen tips like a fool proof way to grill the perfect burger, and must have products like the best cast iron skillet. To feel like a chef in your own kitchen, all you need to do is sign up at Katiecuric dot com slash good Taste. That's ka t i e cic dot com slash good Taste. I promise your taste buds will be happy you did.
All right, we're talking about ice cream Noble prizes for discovering new flavors or or discovering ice cream that doesn't melt.
That's right. Well, you know I would take two blobs of ice cream and accelerate them at high speed and push them together and see if a new flavor comes out.
Well, nobody would give you a Nobel price. But if you can find a solid state ice cream that's permanently solid, then maybe you got something there.
Room temperature ice cream, now there would be an invention.
Well, it's ice you could eat in the winter, maybe, so it's a new kind of material. These topological matter materials because they have interesting conducting and non conducting property. So what are some of the things you can do with them?
Well, one of the most useful immediate applications are to use them to build computer chips. The basis of all modern computing and your phone and your laptop and your iPad and everything use these these little silicon chips that have tiny little circuits, and those circuits are mostly transistors put together in different ways to make logic gates, and those are printed using silicon, which is a fascinating material because you can dope it in one way to make it a conductor, and dope it another way to make it an insulator. So you can print these circuits. One issue is that these things get hot, right as electrons pass through the silicon when it's in its conducting mode, it's not perfectly conducting, and so it heats up a little bit. And if you know, for example, your laptop, right, it gets hot when you're running really complex game on it, and that wastes a lot of heat.
Right, Yeah, I guess that's an effect that I thought I knew how to work, but now I don't because of this conversation. Because I always felt like, Okay, it's electrons going through the copper, and so it's somehow creating some kind of friction and that's where the heat comes from. But how does resistance cause heat?
Well, resistance is when you're taking the motion of the electrons and you're just converting it to the heat of the material. Meaning like you know, an atom absorbs that electron and now that atom is just sort of like has more energy, so you like sped up the motion of that atom, and so instead of the electrons just like sort of surfing along on top of the atoms, some of that energy is sort of like sucked down into the atom and trapped to energize the lattice, to shake up those atoms in the lattice, And that's what you don't want. You want to keep it cold, you want to keep it firm. It doesn't conduct as well when it gets warm also, so it gets worse and worse, and so what you'd like is something which stays cold. It just passes the electricity through it. And not just because they would perform better and faster, but also because it's a huge waste of energy. You know, something like ten percent of our worldwide energy use goes to running computers, and if we can make that more efficient and we can find materials that have less resistance, then these computers can operate more efficiently and they can operate faster and more reliably.
Yeah, if you can take a chunk out of that, you know, ten percent of worldwide energy, you would save a lot.
And so these materials are better conductors than for example, copper is and so that's very promising. Practically speaking, there are big obstacles there, Right, You can't just be like, oh, I have a new complex kind of material which only works in the lab in tiny microducees. Can we now insert it into everyday electronics? You know, if you want to get into like the supply chain for the Apple iPhone, then there's a lot of constraints there. You have to be like cheap and available, you have to be ductiles so you can make wires out of it. So there's a long road to go there, but it's sort of promising.
Maybe give us a sense of how difficult it is to make these materials, Like what's a standard way to make a topological matter conductor? Like using what kind of materials?
Yeah, so originally you have to make them really really thin and have very powerful magnetic fields. These days, people have made three D topological materials, and the way they do it is sort of similar to the way you operate with semic conductors, which is that you add other kinds of things, so you like inject weird things into the crystal lattice to get.
These effects on the surface you mean.
On the surface or in the center also, but you end up getting the same effects.
You mean, you code something like you cod a ceramic with something no.
No, you add like a new kind of material inside the lattice, so that inside the crystal lattice you have, like you know, some other element that's occupying some of these things, and it changes the behavior of the electrons, forcing them, for example, spin locking them, forcing them to move in these circles without having a powerful magnetic field currently. Of course, it takes sort of complex machinery to fabricate these things to make these mixtures. But you know, if we find one that's especially useful, especially powerful, I'm sure it will come up with ways to mass produce them.
Oh, I see, they're not super easy to make yet.
Yeah, they're not super easy to make yet, but that's true of almost everything, right, you know, like the first transistor was not simple or small.
Right, right, and they've gone in smaller and smaller. But now we're sort of reaching the limits of what we can do even with silicon and these crazy powerful ways to make tiny chips. Like, we're reaching a limit and we're going to need something new for wanting to make things even smaller and more powerful.
That's right. We're very used to our computers getting more powerful and smaller every single year. This is Moore's law, where computing power doubles every eighteen months because we can make smaller transistors. But there is a limit there, right, If silicon gets too small, then it loses these properties, it's conductivity and its resistance, and we're pushing up against that limit. So people are working hard to find new materials that we can use to print these transistors. So it's a good time to discover that there's a whole new class of stuff out there that we can design and build that has weird new properties.
Right, right, to make phones even smaller and you know, higher resolution.
And to make your batteries last longer.
Oh that's right. Yeah, if they're more conductive, then you're not wasting as much energy to heat.
Right, Yeah, every time you feel your phone get hot, that's energy from your battery that could have been used to play your Netflix show but instead is heating up your pocket.
But that's just for regular computers that we know. Now, you could also use these materials for a whole new kind of computer.
That's right. We think that they might be excellent as a sort of base material out of which to build quantum computers. Quantum computers, remember, don't have the sort of normal switches that classical computers have, like that are either one or zero, that have these things inside them called cbits, which are in a quantum state, a superposition of ones and zeros with various probabilities. And these quantum computers are really fascinating and have some interesting potential to solve some weird problems. But one of the obstacles to building quantum computers is error correction. These quantum computers can be a little bit noisy and a little bit fuzzy, and you don't always get the answer out that you want, and so they have all these complicated error correcting devices that get more and more laborious, more and more difficult as you get bigger and more powerful computers, which is one reason why we've only ever seen quantum computers with like ten bits or twenty bits. Whereas, for example, you know your phone has megabits and megabits inside of it. We think that potentially these topological materials might have the right ingredients to be sort of self correcting. They might be able to develop cubits that automatically correct themselves.
Right Like if there's an error somehow, that error disappears somehow by itself.
And it comes from the way that the electrons flow in these materials. They're actually sort of symmetries that preserve the electrons in these quasi particles. Remember we talked once about what quasi particles are. Like the way we think of photons as excitations in the electromagnetic field, you can also think about other fields fields inside materials and having energy stored inside those fields. So, for example, like a vibration inside of material, you think of that as like a phonen, like a basic element of the vibration field inside of material. So some of these topological materials have these symmetries that preserve these quasi particles that allow you to build basically self error correcting quantum bits.
I see, Yeah, because these kinds of new kinds of quasi particles can only happen on or special conditions like what you get with these topological materials.
Exactly, And the topological nature of them preserves these symmetries that it forces them to act in certain ways, and those ways help prevent errors from cropping up and correct them when they do.
Right, Because right now, to make a quantum computer, you need like these extreme machines, right, you need like a machine the size of a room just to have ten cubits. But if you can somehow use these tiny materials, then you might get a quantum computer in your pocket.
Yes, you're right, you might, and they might be self air correcting, so you wouldn't need these like really complicated devices to help fix the errors from ten or twenty bits. Currently, the error rate grows very rapidly as you add quantum bits, and so if they're self air correcting, that might solve that problem. But that's sort of like potential. That's something people are exploring. But you know, the flavor of it is that we have a new kind of material and we don't even really know what it can do. Somebody's going to come along next year or the year after and come up with a crazy idea for how you can put these things together to make something nobody's ever imagined.
Mmm.
I see, because it's like opened up a whole new kinds of behaviors of matter that we didn't know before.
Exactly, Like all the complicated behavior of matter that you're familiar with is an emergent phenomena from putting together in complex ways, and now we know there are whole new areas. Like imagine if nobody had ever seen a conductor before, we only ever had insulators, and then you showed up with this material that can like zap people and transmit energy and you know, create these arcs through the area. Like, oh my gosh, it's like magic. This is like that moment when somebody's come up with something new. It's not exactly a conductor, not exactly an insulator. It's something new and weird. It can do new stuff, and so you know what it's going to be able to accomplish might seem like magic to us today.
Wow, interesting in the future will be like this ice cream tastes amazing. What is it? It's a topological material.
Topological mintship is so much better than classical mintship.
Oh my god, yeah, it has mintq chips And you're like, oh my goodness, I can't believe most humans have never tasted a mintqu chip. What a tragedy.
What did it even mean to be human before that was invented? Right? Like, were they even really fully aware?
Life really started when quantum ice cream was invented.
That's what the aliens are waiting for, for us to achieve that level of technology before they come and visit us.
Oh I see, yeah, because they don't want to go anywhere that doesn't have these quantum mint keu chips. It's like, you don't want to go to that place if it doesn't have bathroom. Oh yeah, exactly what kind of occasion is that? All right? Well, again, I think this is an exciting thing because it feels like, you know, we're learning all the time that there are new things yet to be discovered in this universe, like new even new kinds of material and new kinds of matter that we can potentially engineer amazing new devices out of.
That's right, So we have not just revolutions in our basic understanding of the fundamental particles and what the universe is. We also have revolutions all the time, and how those bits fit together to make weird kinds of stuff that exist at our scale. So our understanding the universe is constantly transforming, and there are enormous opportunities out there for people to make discoveries. So you young scientists out there, seven, eight, ten years old, fifteen years old, you can still revolutionize our understanding of the universe. There's so much left to do.
But if you're sixteen, it's over for you, right, is that what you're saying, Daniel? But no, I mean anything could come up of anyone of any age, right.
Yes, absolutely, sixteen year olds could totally revolutionize the universe. I don't know, a's seventeen eighteen a universe haded. No, it's open for everybody. Absolutely, a non exhaustive list of example ages.
Ask yourself, do you want to be in the group of humans that have never seen these revolutions? Or do you want to be in the group of humans the future, humans that know these amazing things? All right, Well, we hope you enjoyed that and it blew your mind a little bit, at least on the surface. Thanks for joining us, See you next time.
Thanks for listening. And remember that. Daniel and Jorge Explain the Universe is a production of iHeart Radio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as dairy dot COM's Last Sustainability to learn more.
Our iHeartRadio Music Festival percentate I Capital one Iming back to Las Vegas September twenty first, a weekend full of superstar performances. Sabracks Come, Look at Bay to Keith, Urban, New Kids on the Block, Paramore, Shoozy, The Black Crows, The Weekend, Thomas Red, Victoria Monett Old plays, Chris Martin, hand More stream live only on Hulu and get it tigguts to be there at AXS dot com.
Hi, I'm David Eagleman from the podcast Inner Cosmos, which recently hit the number one science podcast in America. I mean neuroscientists at Stanford and I've spent my career exploring the three pound universe in our heads.
Join me weekly to explore the relationship.
Between your brain and your life, because the more we know about what's running under the hood.
Be or we can steer our lives.
Listen to Inner Cosmos with David Eagleman on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts.
