15 February 2019

What's a Moiré?

What's a moiré pattern? And why are they one of the hottest things in physics today? Let us explain — with a musical twist.

Scientists love to stack two-dimensional materials like graphene into various arrangements, sometimes adding a twist to create moiré patterns. Still not clear on what moiré patterns are? Mamma mia: Have we got a video for you, created by the whole fields team, with love, for fellow science lovers everywhere.

(Want help with the pointy-headed physics references? Just scroll down the page.)

That's a Moiré!

In Tallahassee, where magnets reign1
With their high fields, here’s what they say:

When graphene2 sheets have a tryst, then you give them a twist, that’s a moiré!3
When patterns that were small undergo quantum sprawl, that’s a moiré!
Electrons zip, zippy-zippy-zay, on their wavy way4, and you’ll say, "Eureka!"
One day you’ll achieve atomic states interleaved5, Signorina!

When 2D allotropes6 spin like kaleidoscopes, that’s a moiré!
Then you turn on high fields, secrets will be revealed: You’re in luck:
When two waves in the mood, double in amplitude, like tsunami,7
Scusami, but you see, back in Tallahassee, that’s a moiré!

When behaviors arise resembling butterflies8, that’s a moiré!
Van der waals9 stick like tape, easy to separate, that’s a moiré!
Electrons spin, spinny-spinny-spin10, in their layers thin, inside your apparatus.11
Then they buzz, buzzy as you please, subatomic bees, through their honeycombed lattice!12

Stack two layers or more, like lasagna al forno: a moiré!
Get the angle just right, by a magical sleight13: You’re in luck:
Majorana fermions14 race around like bustling camerieri!
What a fine recipe for new technology15, that’s a moiré!

Notes

1The National High Magnetic Field Laboratory (National MagLab) is headquartered at Florida State University in Tallahassee.

2This two-dimensional version of carbon boasts amazing properties, including incredible strength, thinness, and very high electrical and thermal conductivity. It has been of keen interest to scientists, engineers and inventors since its discovery in 2004.

3A moiré pattern emerges when one pattern superimposed over another creates an altogether new, larger-scale, regularly repeating pattern. Moiré patterns are found in fabrics, show up when you try to film a film, and emerge when sheets of graphene and other 2D materials are stacked on top of each other in physics experiments.

4At the National MagLab, scientists put materials inside high magnetic fields because the electrons interact with the field in a way that leads to discoveries about that material, its unique properties, and even fundamental physics.

5When two layers of graphene are arranged in a moiré pattern inside a high-field magnet, physicists can observe a “superposition” of both the properties that exist in that arrangement and those that exist in a single layer of graphene. In other words, they are observing the properties of both systems at once.

6Allotropes are different versions of the same element. Diamonds, the graphite used in pencils and graphene are all allotropes of carbon.

7Electrons are both particles and waves. When two electron waves with the same frequency meet at their highest points, they combine to create a wave twice as large as they are. This is called constructive interference.

8In 2013, experiments performed at the National MagLab, using a sample of graphene and boron nitride arranged in a moiré pattern, revealed a fractal energy pattern known as Hofstadter’s butterfly, named after the physicist who predicted it four decades earlier.

9Stacked, 2-D materials are known as van der Waals heterostructures, a reference to the so-called van der Waals forces. These relatively weak forces hold the layers together, but they are easy to separate — so easy, in fact, that scientists can use Scotch tape!

10In addition to moving through a material as current, electrons in a magnet interact with the field with a kind of spinning behavior. They align their spins with the field (like small magnets) and tend to orbit around the magnetic field lines as well.

11The National MagLab is home to many world-record magnets, including the 45-tesla hybrid magnet, the strongest in the world for generating continuous fields. Many a moiré pattern has seen the inside of that unique instrument.

12Graphene and some other 2D materials, including boron nitride, have a hexagonal structure similar to the cells of beehives.

13A team of scientists lead by MIT’s Pablo Jarillo-Herrero discovered in 2018 that by placing one layer of graphene on another at precisely 1.1 degree of difference, they created a moiré pattern that enabled them to observe new behaviors.

14Named after Italian physicist Ettore Majorana, these fermions (a class of subatomic particles) are their own antiparticles! Scientists first looked for them in high-energy particle colliders, but later discovered them in everyday carbon (in thin sheets) using high-field magnets.

15The discoveries coming out of the study of 2D materials in high magnetic fields are contributing to the body of knowledge that will lead to the development of quantum computers and other ground-breaking technologies.

Last modified on 15 February 2019