We’re in a heatwave here, so er I’m in the woods.
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
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
important parts of the subject into a big picture to get you up to speed quickly and

as clearly as possible.
as clearly as possible.

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

lose their electrical resistance.
lose their electrical resistance.

They also have some interesting magnetic properties which allow them to almost magically float,
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.
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,
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.
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.
And as we go, see if you can keep count of all the nobel prizes.

First I need to tell you about magnetic induction.
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
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
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,
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.
and start moving in a circle called an eddy current.

This is called magnetic induction.
This is called magnetic induction.

In a normal metal this current dies away quickly because the material has electrical resistance:
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
the moving electrons bang into the atoms and stop moving, giving up their energy to vibrations

in the atomic lattice warming it up slightly.
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,
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.
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
Like, age of the universe forever according to the theory, and experimentally we’ve

seen currents losing no energy over twenty five years.
seen currents losing no energy over twenty five years.

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

without it losing any energy at all.
without it losing any energy at all.

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

the Meissner effect.
the Meissner effect.

Superconductors expel any magnetic field inside them.
Superconductors expel any magnetic field inside them.

You know how I said that magnetic fields induce electrical currents in conductors.
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.
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
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.
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.
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
So those are the two main features of superconductors, zero electrical resistance and the Meissner

effect.
effect.

And when they were discovered in the early nineteen hundreds physicists were like whoa!
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
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.
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
But first we need to look at exactly what conditions are needed for a superconductor

to superconduct.
to superconduct.

There are three conditions you need for a superconductor, low temperatures, small enough
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
magnetic fields and small enough electrical currents although these two are kind of the

same thing.
same thing.

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

material.
material.

The first superconductors that were studied were pure elements like mercury, aluminium
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
or niobium, and physicists discovered that not all of the elements superconduct, here

are the ones that do.
are the ones that do.

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

they suddenly start superconducting at a sharp phase transition.
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
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
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
they suddenly stop superconducting and go back through the phase transition to a normal

conductor even if they are below the transition temperature.
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
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.
happens to water when it freezes or when it boils.

These are phase transitions too, but those are phase transitions in the material properties,
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.
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,
But it all comes down to what is the configuration of stuff which minimises the overall energy,

known as the gibbs gree 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,
Ifa material will be in a lower energy by freezing into a solid, or turning into a superconductor,

that’s what it will do.
that’s what it will do.

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

say it with me, phase diagrams!
say it with me, phase diagrams!

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

change some global parameters.
change some global parameters.

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

you might have seen before.
you might have seen before.

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

state for different temperatures and magnetic fields of a superconductor.
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
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
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.
of superconductors are used at normal pressure.

Each superconductor has got its own unique phase diagram and filling them in kept a bunch
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.
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,
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
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
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
temperatures with the goal of one day finding a room temperature superconductor and making

tonnes of cash.
tonnes of cash.

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

along the way they have made some startling discoveries.
along the way they have made some startling discoveries.

First of all, in 1935 they discovered type-II superconductors which behave differently to
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.
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
Type-II superconductors behave differently to type-I superconductors when they are in

a magnetic field.
a magnetic field.

Here’s a phase diagram of a type-II superconductor.
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
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
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.
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
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
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,
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.
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
I just threw a load of terminology at you there, so if you are confused just think of

them as a load of sausages.
them as a load of sausages.

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

we’ve found so far.
we’ve found so far.

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

here.
here.

Wikipedia.
Wikipedia.

The next big bombshell to hit the exciting world of superconductivity research was in
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
1986 when researchers made a superconductor made of ceramic which was an insulator before

being cooled down.
being cooled down.

This then led to the discovery of a bunch of high-temperature superconductors.
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
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
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
with just liquid nitrogen at 77 kelvin, which is way cheaper than liquid helium which is

what they had to use before.
what they had to use before.

These new superconductors are known as the cuprates because they contain layers of copper
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.
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,
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
pure carbon based superconductors called fullerenes also known as organic superconductors and

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

People have also squeezed materials between diamond presses and discovered that many materials
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
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
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
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.
it’s not actually practically useful, but still a landmark discovery.

Now on to the theory of superconductivity.
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
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.
materials at the scale of the electrons.

What is the underlying process that allows for zero resistance?
What is the underlying process that allows for zero resistance?

The first theory, Ginzberg-Landau theory predicted properties of superconductors like, which
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
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.
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
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
around them slightly, creating a local positive charge which creates an attractive force between

electrons.
electrons.

So electrons can interact with each other through vibrations in the lattice called phonons
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.
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
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
half particles, and obey the pauli exclusion principle so can’t exist in the same quantum

states.
states.

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

spin zero or spin one.
spin zero or spin one.

Bosons can exist in the same quantum state and so all the cooper pairs form a thing called
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
a condensate which has special properties including not being able to easily absorb

kicks of energy, and so they flow without resistance.
kicks of energy, and so they flow without resistance.

This is known as an energy gap.
This is known as an energy gap.

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

but now you’ve got the basics.
but now you’ve got the basics.

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

because the attractive force from the phonons don’t exist there.
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
So they need some other attractive force between electrons, and we don’t know where that

would come from in high temperature superconductors.
would come from in high temperature superconductors.

For this reason any superconductor that doesn’t follow BCS theory is called an unconventional
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.
superconductor, and the ones that do are called conventional superconductors.

Despite a lot of work going into this high temperature superconductivity is still one
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
of the biggest unsolved mysteries in theoretical condensed matter physics and you’ll probably

win a Nobel prize when you figure it out.
win a Nobel prize when you figure it out.

There are a load of technologies which use superconductors.
There are a load of technologies which use superconductors.

The most widespread use of superconductors is to create large magnetic fields as you
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.
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
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.
material that is cooled down with liquid helium.

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

focus the beams of particles.
focus the beams of particles.

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

process.
process.

And also in other areas where you want to control charged particles like mass spectrometers.
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.
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 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
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.
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
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
magnetic field, where the current and magnetic field are in the superposition state of flowing

in both directions at the same time.
in both directions at the same time.

These josephson junctions can be combined in a specific formation called a superconducting
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
quantum interference device or squid for short, which is a phenomenally sensitive magnetic

field detector, the best humanity has discovered.
field detector, the best humanity has discovered.

These are the detectors that see inside your body in MRI and fMRI machines, they are also
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
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
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
by the josephson junctions to make a tunable qubit: which are the building blocks of superconducting

quantum computers.
quantum computers.

This stuff is my professional background back when I had a proper job, and I think quantum
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.
technology is absolutely fascinating, especially the possible future technologies.

So what does the future hold for superconductors?
So what does the future hold for superconductors?

For a long time people have talked about building transmission lines to transport electricity
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.
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
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
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
yet, so these are the challenges, but it would be cool to be able to ship electricity around

the grid a lot more efficiently.
the grid a lot more efficiently.

You can also use superconductors for levitating things like trains, but this potential has
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,
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.
it’s a thing that exists.

A promising area is to make very efficient superconducting motors or generators for things
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
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.
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
On the quantum devices side, by far the most exciting applications are the range of quantum

computers built with superconducting qubits.
computers built with superconducting qubits.

Now, superconductors aren’t the only way to build quantum computers, but google, IBM,
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
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
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
the quantum mechanics of them, something that can’t currently be done with our most powerful

supercomputers.
supercomputers.

So you could potentially use superconducting qubits to figure out how high temperature
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
superconductivity actually works and then perhaps use that to find a room temperature

superconductor.
superconductor.

In fact, on the research side, figuring out the mechanism of high temperature superconductors
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.
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
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
from the power grid, to consumer electronics as you’d be able to build zero resistance

computers with way lower electricity consumption.
computers with way lower electricity consumption.

But this all depends on the room temperature superconductor also having a high critical
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
current, and critical field, as well as having material properties that make it easy to work

with to fabricate chips.
with to fabricate chips.

Okay so that’s the map of superconductivity.
Okay so that’s the map of superconductivity.

I hope it was informative.
I hope it was informative.

How many Nobel prizes did you count?
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
It should have been 5, which is not bad for one quantum phenomenon, which one of you is

gunna get number six?
gunna get number six?

I’ve made this map available as a digital image on flickr, and poster on my DFTBA store
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.
and if you liked this video please remember to smash the patriarchy.

Especially in physics.
Especially in physics.

Massive shout out to anyone who has bought a poster and to my wonderful patreon supporters.
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,
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
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.
concentrate on making killer content, that’s also bloat free.

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