Electron Quantum Metamaterials: Graphene Superconductors for Power
Every time we think about the future (the one that I will prominently be apart of), we wonder what buildings, cars, and fashion will look like. But not a lot of people think, “what will our climate look like in 2025?”. Realistically, what kind of a climate we will experience in 2050 is something we, to a large degree, are actually in the process of deciding.
Climate in 2050 largely depends on us
The famous quip “prediction is very difficult — especially about the future” is ever more appropriate when we want to predict future Earth conditions as the climate in 2050 will depend, to a very large degree, on decisions we make now and in the immediate future.
Climate is controlled by how much of the Sun’s heat energy arrives at, and remains near, the Earth’s surface. Scientists tell us that we can expect no major changes in heat arriving from the Sun for many thousands of years to come. So the changes we will see in climate from now until 2050 will mostly be related to how much of the arriving heat stays here.
This is where our greenhouse gas (GHG) waste (“emission”) becomes important. The greater the concentration of these gases in the atmosphere, the more heat is retained near the Earth and the higher the global average temperature will be.
How hot could it get?
Global political leaders have agreed in the Paris Climate Agreement that we, will reduce our GHG emissions to the point that human-caused global warming will never raise the average annual global air temperature by more than two degrees Celsius. But…human-caused global warming is estimated to reach around three degrees, so how will this work?
The chances of meeting this goal are difficult with our current trajectory — a recent report even went as far as to say that we have a 5% chance of remaining global warming to within two degrees.
What happens if Earth gets 2°C warmer?
It all started in 1975 with, surprisingly, an economist. Dr. William Nordhaus saw the warming planet as a threat to the global economy. He asked his colleagues in the International Institute “Can We Control Carbon Dioxide?” Nordhaus said an increase in the global average temperature of 2°C (caused by man-made carbon dioxide) would change our climate in ways never seen before.
Nordhaus didn’t make the 2°C up, he based it on science. Since he knew carbon dioxide was warming the planet, Nordhaus calculated what would happen if the concentration in the atmosphere was doubled — which is basically a global increase of 2°. He also predicted that, at the then-current rates, we were headed for “the danger zone” beyond 2°C around the year 2030.
Forest Fires will increase:
So will droughts:
AND floods from an imbalance in different parts of the earth:
And if we warm by 2°C, the world will be a lot drier, which will impact economies, agriculture, infrastructure, and weather patterns. Rising temperatures will damage ecosystems and species that cannot adapt, including those in coral reefs and Arctic areas. Low-lying coastal regions and small islands worldwide are at risk of disappearing from melting ice and more disasters will occur.
I’m sure we’d all much rather see our earth like this:
So what do we do to get there? Let’s dive deeper into how we produce energy and power on earth.
Renewable Energy — fossil fuel biggest factor to emissions.
89% of emissions came from fossil fuels and industry. The continued use of fossil fuels for power generation has led to an increased interest in clean, green and non-polluting sources of renewable energy, such as solar, hydropower, geothermal, biomass and wind. Integration of renewables does still pose challenges such as intermittency of the resources, connection to grid, interconnects from remote generation locations, and comparative cost vs. fossil fuel generation.
So the question is — how can we create a scalable solution to generate renewable energy all around the world?
Lucky for us, we can do this using a field in nanotechnology called metamaterials, superconductivity, and graphene.
Squeezed graphene = superconductor
Twisted bilayer graphene can be made into a superconductor by simply squeezing the two layers closer together. The causes of correlated electron phenomena in bilayer graphene could help to unravel the puzzle of unconventional superconductivity.
This superconductivity can help provide electricity for ultra-fast levitating trains and solar panels that could power homes in slums.
Now, this is probably what you’re thinking:
Before I go into how this will work. Let’s first understand what graphene is and it’s properties.
Graphene — evolutionary material
Graphene is a sheet of carbon just one atom thick BUT it has remarkable electronic properties which have allowed physicists to do a lot with the free-standing material since 2004.
There is very weak coupling between electrons in bilayers of graphene. The electronic properties of a bilayer are strongly influenced by the relative orientation of its two graphene sheets. When two layers are twisted by a “magic angle” of about 1.1° relative to each other, “flat bands” occur which makes the kinetic energy of the electrons almost independent of their momentum.
If the band is very flat, even the most energetic electrons have very low kinetic energy. This is really interesting in systems that are more dominated by electron-electron interaction energy. Systems can often do exotic things to minimize that interaction energy.
Graphene is usually an extremely good electrical conductor, but when the flat bands are exactly half filled with electrons, the bilayer behaves like an insulator. This can be seen with the localization of electrons by electron-electron interactions between the graphene layers. By injecting or withdrawing electrons from this correlated insulator, you can produce electron-doped or hole-doped superconductors respectively.
Many features of this superconductivity are the same as type-II superconductors like cuprates and pnictides which are superconductors that remain at relatively high temperatures and magnetic field strengths.
The mechanism for type-II superconductivity is fairly elusive. This is mainly because it’s difficult to change anything in the system, such as doping or lattice constant without making a completely new material. Creating changes also creates changes in other parts of the material. This has complicated efforts to optimize type-II materials and produce room-temperature superconductors.
We can now use bilayer graphene — with twist angle 1.1°. These show superconductivity before being compressed whereas those with greater twist angles did not. But, when pressure was applied to samples with twist angles greater than 1.1°, the bilayers became superconductors.
The Magic Angle
This angle is related to the nature of the interlayer coupling, which is changed by compressing the bilayer at pressures greater than 10,000 atm. The critical temperature of the superconductor also increases slightly from 1 K to 3 K.
These systems are incredibly tunable. We can go from superconducting to metal to insulating states over large ranges of temperature, pressure and magnetic field without changing the composition.
Breakdown of the process
I made this drawing to breakdown the simple idea.
Still don’t get it?
So basically atoms in the same graphene sheet have a very strong bond and atoms in different sheets have a very weak bond. This is why we can create large single sheets of graphene and then layer them on top of each other.
If you rotate one graphene sheet in respect to the other (1.1°), you can create a moire lattice, a periodic pattern that forms within the twisted layers. The moire pattern creates a new landscape for electrons to move through, making it possible for us to finetune them at the atomic level.
Electrons react very sensitively to minor changes in the twist angle between graphene sheets giving us the ability to induce superconductivity — which the most powerful form of electrified conductor because it has zero electrical resistance.
Wanna learn some more?
I made a quick video highlighting some of the same stuff in this video:
Now let’s continue.
Energy-efficient superconducting cable for future
As electricity flows through normal metals, electrons bump into each other and the crystal structure walls they flow through makes them loose a lot of energy (high resistance).
But in some remarkable materials known as superconductors, when cooled below a characteristic superconducting temperature, electrons pair up and coalesce into a massive quantum wave, now flowing in coherent motion, without losing any energy at all.
This is why superconductors can be very useful for creating power. By applying pressure to selected non-superconducting materials we can turn them into new superconducting materials, almost by quantum alchemy. This approach has already yielded superconducting temperatures above 200 degree Kelvin (around -73°C), and now with graphene is expected to yield new and exciting superconducting families of materials.
Although there are many potential applications. For example, the most advanced technology to make prototype quantum computers today are based on superconducting devices. Magic-angle graphene superlattices could be a new type of electrically tunable superconductor. Superconductors can also be used in many other applications, such as ultrasensitive detectors of light.
There is no doubt that graphene is an exceptional material in so many ways. Its unique properties, such as extremely high mechanical strength (it is stronger than steel) and extremely high electrical conductivity, with electrons zipping through it at near-ballistic speeds, have been known for a while now. Researchers had already shown that it could behave like a superconductor before too BUT the superconductivity was only observed when it was in contact with other superconducting materials.
I’m Alishba Imran.
I am a Blockchain, VR and Machine Learning developer interested in medicine and healthcare. If you want to stay up to date with my progress feel free to follow me on LinkedIn, and Medium! If you enjoyed reading this article, please press the👏 button, and share!