The Map of Superconductivity

Summary

This script offers an insightful exploration into the world of superconductivity, detailing the unique properties of superconductors, such as zero electrical resistance and the Meissner effect. It delves into the history, types, and theories behind superconductors, including the groundbreaking BCS theory and the enigma of high-temperature superconductivity. The script also highlights practical applications, from MRI machines to quantum computing, and speculates on future technologies, emphasizing the potential impact of room temperature superconductors on various industries.

Takeaways

• 🌡️ Superconductors are materials that lose electrical resistance when cooled to low temperatures and exhibit unique magnetic properties.
• 🔁 Eddy currents in superconductors can flow indefinitely due to the absence of electrical resistance, unlike in normal metals.
• 🌀 The Meissner effect describes how superconductors expel magnetic fields by creating currents that cancel out the external field.
• 🔍 There are two main types of superconductors: Type-I and Type-II, with Type-II allowing magnetic fields to penetrate in specific points called vortices.
• 🏆 The study of superconductivity has led to multiple Nobel Prizes, highlighting its significance in physics.
• ❄️ Superconductivity requires low temperatures, small magnetic fields, and small currents, with specific thresholds for each material.
• 📈 The search for new superconductors aims to find materials with higher transition temperatures, potentially leading to room-temperature superconductors.
• 🧠 The BCS theory explains conventional superconductivity through electron pairing facilitated by lattice vibrations (phonons), but it does not account for high-temperature superconductivity.
• 🛠️ Superconductors have numerous applications, including MRI machines, particle accelerators, and quantum devices like SQUIDs and qubits for quantum computing.
• 🚀 The future of superconductivity could involve more efficient energy transmission, levitation technologies, and advancements in quantum computing.
• 🏁 The discovery of a practical room-temperature superconductor could revolutionize electronics and power grids by enabling zero-resistance components.

Q & A

What are superconductors and what happens when they are cooled down to a low temperature?

Superconductors are materials that, when cooled down to a low temperature, lose their electrical resistance. They also exhibit magnetic properties that allow them to expel magnetic fields and float, which is a phenomenon explained by quantum mechanics.

What is magnetic induction and how does it differ in superconductors compared to normal metals?

Magnetic induction is the process where a changing magnetic field induces a current in a conductor. In a normal metal, these currents quickly die away due to electrical resistance. However, in superconductors, due to the absence of electrical resistance, the induced eddy currents can continue flowing indefinitely.

What is the Meissner effect and why is it significant in superconductors?

The Meissner effect is a phenomenon where superconductors expel any magnetic field from their interior. This occurs because the eddy currents generated within the superconductor create magnetic fields that cancel out the external magnetic field, a quantum effect not observed in normal conductors.

What are the three conditions necessary for a superconductor to exhibit superconductivity?

The three conditions necessary for superconductivity are low temperatures, small enough magnetic fields, and small enough electrical currents. The specific values for these conditions depend on the material.

What is the significance of the transition temperature in superconductors?

The transition temperature is the specific temperature at which a material undergoes a phase change and begins to superconduct. This is a sharp and sudden change, and it's a critical parameter in determining the superconducting state of a material.

What are type-I and type-II superconductors, and how do they differ in their behavior in a magnetic field?

Type-I superconductors expel magnetic fields entirely when below their critical temperature. Type-II superconductors, on the other hand, allow the magnetic field to penetrate in a specific pattern called vortices under certain conditions, while still maintaining superconductivity in the rest of the material.

What is the BCS theory and how does it explain superconductivity?

The BCS theory is a microscopic theory of superconductivity that explains how electrons can pair up into composite entities known as Cooper pairs through interactions with lattice vibrations called phonons. These pairs can then form a condensate, which allows them to flow without resistance, leading to superconductivity.

Why is high-temperature superconductivity still a mystery, and what is its significance?

High-temperature superconductivity is a mystery because the BCS theory, which relies on phonons for the attractive force between electrons, does not apply to these materials. The source of the attractive force in high-temperature superconductors is unknown, and solving this mystery could lead to the discovery of room-temperature superconductors.

What are some practical applications of superconductors mentioned in the script?

Superconductors are used in MRI machines to create strong magnetic fields, in particle accelerators for controlling particle beams, in some nuclear fusion reactors for plasma control, and in quantum devices such as SQUIDs for sensitive magnetic field detection and in quantum computers for creating qubits.

What are the potential future applications of superconductors in technology and energy?

Future applications of superconductors could include efficient transmission lines for electricity, levitating trains, superconducting motors or generators for renewable energy, and advancements in quantum computing to simulate quantum mechanics for new material discoveries.

What is the significance of the number of Nobel Prizes mentioned in the script, and what does it imply about superconductivity?

The mention of five Nobel Prizes signifies the importance and impact of superconductivity research. It implies that the phenomenon of superconductivity has been a significant area of study with profound implications for physics and technology, and further advancements could lead to additional recognition.

Outlines

00:00

🔌 Introduction to Superconductivity

The script opens with an introduction to superconductivity, a phenomenon where materials lose electrical resistance at low temperatures. It explains the basics of superconductors, their magnetic properties, and the potential for levitation. The narrator outlines the structure of the video, which includes an exploration of different types of superconductors, their properties, the underlying theory, applications, and future research directions. The concept of magnetic induction and the behavior of eddy currents in superconductors versus normal metals are also introduced, highlighting the perpetual flow of current in superconductors due to the absence of electrical resistance.

05:02

🧲 Superconductor Properties and Phase Transitions

This paragraph delves into the properties of superconductors, focusing on their unique response to magnetic fields, known as the Meissner effect, where they expel magnetic fields. The conditions required for superconductivity are discussed, including low temperatures, small magnetic fields, and small electrical currents. The concept of phase transitions in superconductors is compared to familiar examples like water freezing or boiling. The paragraph also introduces phase diagrams that illustrate the relationship between temperature, magnetic fields, and the superconducting state. The historical progression of superconductor research and the discovery of type-I and type-II superconductors are outlined, with type-II allowing for magnetic field penetration in the form of vortices.

10:04

🌡 The Evolution of Superconductor Research

The script continues with a historical overview of superconductor research, highlighting the discovery of higher temperature superconductors and the introduction of unconventional materials such as ceramics. The discovery of cuprates, pnictides, fullerenes, and the recent 2020 discovery of a room temperature superconductor under high pressure are mentioned. The paragraph also touches on the theoretical understanding of superconductivity, starting with the Ginzberg-Landau theory and moving to the BCS theory, which explains the formation of Cooper pairs and the energy gap that leads to zero resistance. However, the BCS theory does not account for high-temperature superconductivity, which remains a mystery.

15:04

🛠️ Applications and Future of Superconductivity

The final paragraph discusses the practical applications of superconductors, including their use in MRI machines, particle accelerators, and quantum devices like SQUIDs and Josephson junctions. The potential for superconductors in energy transmission, levitating trains, and renewable energy through efficient motors and generators is explored. The paragraph also speculates on the future of quantum computing with superconducting qubits, suggesting that advancements in this field could lead to a better understanding of high-temperature superconductivity. The script concludes with the potential impact of room temperature superconductors on electronics and the power grid, emphasizing the ongoing research and the possibility of revolutionary changes.

🏆 Conclusion and Acknowledgements

The video concludes with a summary of the information presented and a playful prompt for viewers to count the number of Nobel Prizes mentioned, which is five. The narrator offers the map of superconductivity as a digital image and poster, encourages viewer support, and thanks patrons for their contributions. The script ends with a call to action for supporting educational content and a humorous note about decoupling from the YouTube algorithm to focus on content creation.

Keywords

💡Superconductivity

Superconductivity refers to the phenomenon where certain materials, when cooled to very low temperatures, exhibit zero electrical resistance, allowing electric current to flow without energy loss. In the video, this concept is central as it discusses the properties, types, and applications of superconductors, such as their ability to float due to magnetic properties and their use in MRI machines and quantum computing.

💡Eddy Currents

Eddy currents are circular electric currents induced within a conductor when it is exposed to a changing magnetic field. The script explains that in a normal metal, these currents quickly dissipate due to electrical resistance, but in a superconductor, they can flow indefinitely without energy loss, illustrating the unique properties of superconductors.

💡Meissner Effect

The Meissner effect is a quantum phenomenon observed in superconductors where the material expels an applied magnetic field. The video describes this effect as a key feature of superconductors, showing how superconductors can cancel out external magnetic fields with internally generated fields, which is crucial for applications like magnetic levitation trains.

💡Phase Transition

A phase transition is a change in the state of matter, such as from solid to liquid or gas. In the context of the video, superconductivity is described as a phase transition at the electronic level, where materials undergo a change in their electronic properties at a critical temperature, leading to the onset of superconductivity.

💡Critical Field and Critical Current

The critical field and critical current are thresholds that, when exceeded, cause a superconductor to revert to its normal state. The script mentions these terms to explain the limits under which a superconductor can maintain its zero resistance state, which is important for understanding the practical applications and limitations of superconducting materials.

💡Type-I and Type-II Superconductors

Type-I and Type-II superconductors are classifications based on their behavior in a magnetic field. The video script explains that Type-I superconductors expel all magnetic fields, while Type-II superconductors allow limited penetration in the form of vortices, which is a significant distinction in their applications and properties.

💡Cooper Pairs

Cooper pairs are pairs of electrons that, through interaction with the lattice structure of a material, can move together without resistance in a superconductor. The script uses this concept to explain the microscopic mechanism behind superconductivity, as described by the BCS theory.

💡BCS Theory

The BCS theory, named after its creators Bardeen, Cooper, and Schrieffer, is the microscopic theory that explains conventional superconductivity. The video mentions this theory to describe how electrons form Cooper pairs, which then condense into a state that allows for zero resistance in superconductors.

💡High-Temperature Superconductors

High-temperature superconductors are materials that exhibit superconductivity at temperatures higher than conventional superconductors, though still far below room temperature. The script discusses the discovery of these materials, such as cuprates and pnictides, and their significance in the search for room-temperature superconductivity.

💡Quantum Computers

Quantum computers are advanced computational devices that use quantum bits or qubits to perform operations. The video script highlights the use of superconducting materials to create qubits, which are essential components of quantum computers, indicating the potential of superconductivity in advancing computational technologies.

💡Josephson Junctions

Josephson junctions are components in superconducting circuits that allow for quantum tunneling of Cooper pairs between superconductors. The script explains their role in creating superpositions of current and magnetic fields, which are vital for sensitive detectors like SQUIDs and for building quantum computers.

Highlights

Superconductors are materials that lose electrical resistance when cooled to low temperatures and exhibit unique magnetic properties.

Superconductors can float due to their magnetic properties, explained by quantum mechanics rather than magic.

Magnetic induction in superconductors results in eddy currents that can flow indefinitely due to zero electrical resistance.

The Meissner effect describes how superconductors expel magnetic fields through induced eddy currents.

Three conditions are necessary for superconductivity: low temperatures, small magnetic fields, and small electrical currents.

Superconductors undergo a sharp phase transition at a critical temperature, turning into a superconducting state.

Phase diagrams are used to represent the conditions under which a material becomes superconducting.

Type-II superconductors allow magnetic fields to penetrate in specific points called vortices, unlike Type-I superconductors.

The discovery of high-temperature superconductors, such as cuprates, has been significant in advancing the field.

The Ginzburg-Landau theory and BCS theory provide the foundational understanding of superconductivity.

Cooper pairs and the concept of energy gaps are central to the BCS theory of superconductivity.

High-temperature superconductors do not follow the BCS theory, making them unconventional and a subject of ongoing research.

Superconductors are used in MRI machines, particle accelerators, and other technologies requiring strong magnetic fields.

Josephson junctions and SQUIDs are quantum devices that leverage superconducting properties for sensitive detection and quantum computing.

Future applications of superconductors include potential uses in energy transmission, levitation technology, and quantum computing.

The discovery of room temperature superconductors, although under high pressure, marks a significant milestone in the field.

The search for a room temperature and room pressure superconductor continues, which could revolutionize electronics and power grids.

The video transcript mentions five Nobel prizes associated with superconductivity, highlighting its impact on science.

Transcripts

We’re in a heatwave here, so er I’m in the woods.

Hello everyone this is the map of superconductivity, where, as ever, I’ve broken down all the

important parts of the subject into a big picture to get you up to speed quickly and

as clearly as possible.

Superconductors are materials which, when you cool them down to a low temperature, they

lose their electrical resistance.

They also have some interesting magnetic properties which allow them to almost magically float,

but it’s not magic, it’s just plain old quantum mechanics.

We’ll look at the different kinds of superconductors, their properties, the theory behind them,

their applications in the real world, and the future avenues of research and technology.

And as we go, see if you can keep count of all the nobel prizes.

First I need to tell you about magnetic induction.

If you have a conducting material, which is a material that has electrons that can move

around freely, like a piece of metal at room temperature, and you move a permanent magnet

near to it, these electrons feel this changing magnetic field, they feel a force from it,

and start moving in a circle called an eddy current.

This is called magnetic induction.

In a normal metal this current dies away quickly because the material has electrical resistance:

the moving electrons bang into the atoms and stop moving, giving up their energy to vibrations

in the atomic lattice warming it up slightly.

But if you do the same thing to a superconductor, because they have got zero electrical resistance,

the eddy current will never stop flowing and will carry on circulating forever.

Like, age of the universe forever according to the theory, and experimentally we’ve

seen currents losing no energy over twenty five years.

Zero electrical resistance also means you can pass a direct current through a superconductor

without it losing any energy at all.

That’s cool, but they have another important property to do with magnetic fields called

the Meissner effect.

Superconductors expel any magnetic field inside them.

You know how I said that magnetic fields induce electrical currents in conductors.

Well the opposite is also true, any electrical current creates a magnetic field.

If a superconductor is in a magnetic field, it gets a load of eddy currents which create

their own magnetic fields that exactly cancel out and expel the original magnetic field.

This is a quantum effect and doesn’t happen in normal conductors.

So those are the two main features of superconductors, zero electrical resistance and the Meissner

effect.

And when they were discovered in the early nineteen hundreds physicists were like whoa!

and then since then they have investigated more and made a load of useful technology

out of them which we’ll look at in a bit.

But first we need to look at exactly what conditions are needed for a superconductor

to superconduct.

There are three conditions you need for a superconductor, low temperatures, small enough

magnetic fields and small enough electrical currents although these two are kind of the

same thing.

The specific temperature and magnetic field that breaks superconductivity depends on the

material.

The first superconductors that were studied were pure elements like mercury, aluminium

or niobium, and physicists discovered that not all of the elements superconduct, here

are the ones that do.

For each material as you cool them down they undergo a sharp transition temperature where

they suddenly start superconducting at a sharp phase transition.

Then when they are in the superconducting state if you apply a larger and larger magnetic

field or larger and larger current they have a critical field or critical current where

they suddenly stop superconducting and go back through the phase transition to a normal

conductor even if they are below the transition temperature.

Even if all of this is new you already know about phase transitions, because this is what

happens to water when it freezes or when it boils.

These are phase transitions too, but those are phase transitions in the material properties,

whereas the superconducting phase transitions are transitions in the electronic properties.

But it all comes down to what is the configuration of stuff which minimises the overall energy,

known as the gibbs gree energy.

Ifa material will be in a lower energy by freezing into a solid, or turning into a superconductor,

that’s what it will do.

Anyway, as any fan of physics knows, when we have phase transitions we’re gunna have,

say it with me, phase diagrams!

These are very handy graphs because they show us what state your thing will be in when you

change some global parameters.

This is a phase diagram for the state of water when you change temperature and pressure which

you might have seen before.

And here is the analogous example for the superconducting state and normal conducting

state for different temperatures and magnetic fields of a superconductor.

This also changes with pressure as well, but I’m not plotting that here because it’d

need a 3D plot, and superconductivity at pressure is a bit of a research niche, the vast majority

of superconductors are used at normal pressure.

Each superconductor has got its own unique phase diagram and filling them in kept a bunch

of experimental physicists happily busy for years as they filled in all the points.

And they didn’t just stick to the elements, they started looking at compound materials,

of which there are an infinite amount, and the search for new superconductors has been

going on ever since in an attempt to find materials with higher and higher transition

temperatures with the goal of one day finding a room temperature superconductor and making

tonnes of cash.

Here’s a plot of the discovery of higher and higher temperature superconductors, and

along the way they have made some startling discoveries.

First of all, in 1935 they discovered type-II superconductors which behave differently to

the superconductors I’ve described so far, which were then called type-I superconductors.

Type-II superconductors behave differently to type-I superconductors when they are in

a magnetic field.

Here’s a phase diagram of a type-II superconductor.

Down here it still behaves just like a type-I superconductor, but then they have an intermediate

state where they do let the magnetic field penetrate them, but only in specific points

in a formation called a magnetic field vortex, or vortices for short.

Here the bulk of the material is still superconducting, but at these thread like vortices the material

is a normal conductor, the magnetic field goes all the way through in a certain small

amount called a magnetic flux quanta, and each one is surrounded by a swirling supercurrent,

which is the name for the electrical current in a superconductor.

I just threw a load of terminology at you there, so if you are confused just think of

them as a load of sausages.

And you’ll be pleased to hear that these are the only two kinds of superconductors

we’ve found so far.

There is a kind of type-1.5 superconductor, but I can’t be bothered to talk about them

here.

Wikipedia.

The next big bombshell to hit the exciting world of superconductivity research was in

1986 when researchers made a superconductor made of ceramic which was an insulator before

being cooled down.

This then led to the discovery of a bunch of high-temperature superconductors.

Although high-temperature is a little bit of a misnomer, because they still have to

be cooled way below zero with cryogenic liquids but now you can make a thing superconduct

with just liquid nitrogen at 77 kelvin, which is way cheaper than liquid helium which is

what they had to use before.

These new superconductors are known as the cuprates because they contain layers of copper

oxide, with a load of other stuff in there as well.

And there’s also many other types of superconductor iron based superconductors called the pnictides,

pure carbon based superconductors called fullerenes also known as organic superconductors and

there is others as well, but you get the picture.

People have also squeezed materials between diamond presses and discovered that many materials

start superconducting when they are at very high pressure and recently in 2020 a room

temperature superconductor was discovered called Carbonaceous sulfur hydride which superconducts

at 15 celsius, but only under a huge amount of pressure squeezed in a diamond press, so

it’s not actually practically useful, but still a landmark discovery.

Now on to the theory of superconductivity.

It was not an easy job to figure out the underlying theory of what is actually going on in superconducting

materials at the scale of the electrons.

What is the underlying process that allows for zero resistance?

The first theory, Ginzberg-Landau theory predicted properties of superconductors like, which

would be type one and type two, but this was superseded by a microscopic theory called

BCS theory, named after the initials of the creators.

They figured out that, as electrons move through the lattice of atoms, they attract the atoms

around them slightly, creating a local positive charge which creates an attractive force between

electrons.

So electrons can interact with each other through vibrations in the lattice called phonons

and this allows them to pair up into a composite entity known as a Cooper pair.

Now, if you’ve watched my map of particle physics you’ll know that electrons are spin

half particles, and obey the pauli exclusion principle so can’t exist in the same quantum

states.

But the cooper pairs behave like bosons, because when you add their spins together you get

spin zero or spin one.

Bosons can exist in the same quantum state and so all the cooper pairs form a thing called

a condensate which has special properties including not being able to easily absorb

kicks of energy, and so they flow without resistance.

This is known as an energy gap.

That’s just a very quick explanation because a full description would take a long time,

but now you’ve got the basics.

What is interesting is this theory doesn’t explain high temperature superconductivity

because the attractive force from the phonons don’t exist there.

So they need some other attractive force between electrons, and we don’t know where that

would come from in high temperature superconductors.

For this reason any superconductor that doesn’t follow BCS theory is called an unconventional

superconductor, and the ones that do are called conventional superconductors.

Despite a lot of work going into this high temperature superconductivity is still one

of the biggest unsolved mysteries in theoretical condensed matter physics and you’ll probably

win a Nobel prize when you figure it out.

There are a load of technologies which use superconductors.

The most widespread use of superconductors is to create large magnetic fields as you

can circulate a lot of current in a loop without burning any energy.

This is what the big tube is in MRI machines, that is basically coils and coils of superconducting

material that is cooled down with liquid helium.

Superconducting magnets are also extensively used in particle accelerators to bend and

focus the beams of particles.

They have been used in some tokamak reactors to control the plasma in the nuclear fusion

process.

And also in other areas where you want to control charged particles like mass spectrometers.

There are also many kinds of quantum devices which use superconductors.

The most useful are josephson junctions, which are small gaps between superconductors where

the cooper pairs can still flow across the gap through quantum tunneling, and so you

get a continuous flow of current even with no voltage applied.

You can use this to set up superpositions of current, and therefore superpositions of

magnetic field, where the current and magnetic field are in the superposition state of flowing

in both directions at the same time.

These josephson junctions can be combined in a specific formation called a superconducting

quantum interference device or squid for short, which is a phenomenally sensitive magnetic

field detector, the best humanity has discovered.

These are the detectors that see inside your body in MRI and fMRI machines, they are also

set the voltage standard in fundamental physics, are used as efficient radio frequency antennas

in research and in mobile phone masts, and you can use the superposition of states created

by the josephson junctions to make a tunable qubit: which are the building blocks of superconducting

quantum computers.

This stuff is my professional background back when I had a proper job, and I think quantum

technology is absolutely fascinating, especially the possible future technologies.

So what does the future hold for superconductors?

For a long time people have talked about building transmission lines to transport electricity

through superconductors to significantly reduce the amount of energy that is lost.

But to be cost effective it’d need to be a superconductor that you don’t need to

cool down very much, which can carry high currents and is strong, we don’t have this

yet, so these are the challenges, but it would be cool to be able to ship electricity around

the grid a lot more efficiently.

You can also use superconductors for levitating things like trains, but this potential has

been around for a while so I’m not sure there is a great need for it, but you know,

it’s a thing that exists.

A promising area is to make very efficient superconducting motors or generators for things

like wind turbines which could potentially decrease the cost of the electricity they

generate, so this would be really cool, to make renewable energy even cheaper.

On the quantum devices side, by far the most exciting applications are the range of quantum

computers built with superconducting qubits.

Now, superconductors aren’t the only way to build quantum computers, but google, IBM,

D-Wave and others have built very advanced superconducting quantum computers which could

potentially be used to understand and find new superconducting materials by simulating

the quantum mechanics of them, something that can’t currently be done with our most powerful

supercomputers.

So you could potentially use superconducting qubits to figure out how high temperature

superconductivity actually works and then perhaps use that to find a room temperature

superconductor.

In fact, on the research side, figuring out the mechanism of high temperature superconductors

and whether a room temperature and room pressure superconductor can exist, would be fantastic.

If we had a room temperature superconductor it could potentially revolutionise all electronics

from the power grid, to consumer electronics as you’d be able to build zero resistance

computers with way lower electricity consumption.

But this all depends on the room temperature superconductor also having a high critical

current, and critical field, as well as having material properties that make it easy to work

with to fabricate chips.

Okay so that’s the map of superconductivity.

I hope it was informative.

How many Nobel prizes did you count?

It should have been 5, which is not bad for one quantum phenomenon, which one of you is

gunna get number six?

I’ve made this map available as a digital image on flickr, and poster on my DFTBA store

and if you liked this video please remember to smash the patriarchy.

Especially in physics.

Massive shout out to anyone who has bought a poster and to my wonderful patreon supporters.

You are all helping me keep making educational content which is free for anyone to watch,

and also helping me to decouple myself from the fickle youtube algorithm so that I can

concentrate on making killer content, that’s also bloat free.

So thank you so much and I’ll see you on the next video.