Gyroscopes lead scientists to unusual state of matter in a disorganized structure

January 15, 2018, University of Chicago
UChicago scientists crafted a structure that displays unusual waves--which can even be directed into particular shapes. Credit: Noah Mitchell/University of Chicago

You don't have to be perfectly organized to pull off a wave, according to University of Chicago scientists.

Using a set of gyroscopes linked together, physicists explored the behavior of a material whose structure is arranged randomly, instead of an orderly lattice. They found they could set off one-way ripples around the edges, much like spectators in a sports arena—a "topological wave," characteristic of a particularly unusual state of matter.

Published Jan. 15 in Nature Physics, the discovery offers new insight into the of collective motion and could one day have implications for electronics, optics or other technologies.

The team, led by Assoc. Prof. William Irvine, used gyroscopes—the top-like toys you played with as a kid—as a model system to explore physics. Because gyroscopes move in three dimensions, if you connect them with springs and spin them with motors, you can observe all kinds of things about the rules that govern how objects move together.

Two years ago, the team observed an odd behavior in their gyroscopes: at certain frequencies, they could set off a wave that traveled around the edges of the material in one direction only. This was strange, but had some counterparts in other branches of physics. It's a behavior characteristic of a recently discovered state of matter called a .

But next, trying to find which conditions were truly essential, they modified the pattern of the gyroscopes. Where before the gyroscopes had been neatly lined up in equally spaced rows, like the lattice pattern in a crystal, Irvine and team scattered the points randomly around.

At the right frequency, researchers can direct a wave only around the outer edges of a neatly ordered lattice of gyroscopes. But to their surprise, researchers found the waves also appear if the gyroscopes don't have a neat lattice. Credit: Noah Mitchell/University of Chicago

They turned the on, and still saw the waves.

This is exceedingly strange. Traditionally, the lattice order is very important in physical properties. It's a bit like if every time you tossed a handful of puzzle pieces on the table, it still made a recognizable image.

"Everything up to this point was engineered. We thought you had to build a particular lattice, and that determines where the wave goes," said Irvine. "But when we asked what happened if you took away the spatial order, no crystal plane, no clear structure...the answer's yes. It just works."

"A collective behavior with local roots is also really interesting because that's a much easier way to manufacture a material," said graduate student Noah Mitchell, the first author on the paper. "It was thought spatial order had to be globally coordinated, but the fact that local properties are sufficient could open a lot of possibilities."

There are many in the everyday world that don't have a crystalline structure, including Styrofoam, glass, foam, plastic and rubber. The physics behind these systems is less understood than their crystalline counterparts, but as scientists' ability to engineer them—including as quantum systems and metamaterials—grows, they are increasingly of interest. If these amorphous materials could display some of the properties of crystals, it could lay the foundations for new technologies.

Explore further: 'Gyroscope' molecules form crystal that's both solid and full of motion

More information: Noah P. Mitchell et al, Amorphous topological insulators constructed from random point sets, Nature Physics (2018). DOI: 10.1038/s41567-017-0024-5

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mackita
3 / 5 (2) Jan 15, 2018
Amorphous topological insulators are known for quite some time - so that the above observation may not come as so big surprise. They merely tried to simulate them by spin lattice. The precession of gyroscopes would correspond so-called Dirac cones.
Nik_2213
not rated yet Jan 15, 2018
Hmmm... Next 'geek toy' ??
mackita
not rated yet Jan 15, 2018
The description of the above picture would be: Combining kagomized (upper) and Voronoized (lower) networks at an arbitrary boundary — here taken to be a boundary spelling 'CHERN' numbers — provides a unidirectional waveguide (animation). Shaking a single gyroscope at the left sends an excitation confined to the sinuous boundary across the sample. Topological insulators are known to be an unidirectional conductors of spin currents (which is known as an unidirectional spin Hall magnetoresistance).
mackita
not rated yet Jan 15, 2018
You may think that this study is of completely abstract nature, but it isn't : before some time Ruslan Prozorov from Ames Labs did observe similar flux patterns in thin layers of Pb superconductor (see also here). Unfortunately most of his suprafroth videos disappeared from the web.
mackita
not rated yet Jan 15, 2018
Another analogy, this time acoustic one: Silicon water stimulated with unltrasound found to behave like a topological insulator With his team, Huber created a 10 x 10 centimetre silicon wafer that consists of 100 small plates connected to each other via thin beams. The key aspect is that when the wafer is stimulated using ultrasound, only the plates in the corners vibrate; the other plates remain still, despite their tight connections.
Parsec
not rated yet Jan 15, 2018
I suggest that anyone that doesn't realize just how surprising and unusual this behavior is to reread the article. Essentially, the behavior not only reproduced topological insulator property in an entirely unique model, but they didn't have any of the kinds of requirements that are normally associated with topological or boundary waves. This implies that these kinds of devices can be created with a great deal more flexibility.
Whydening Gyre
not rated yet Jan 15, 2018
FTA;
"Because gyroscopes move in three dimensions"
I'm not quite gettin' how they are moving in 3 dimensions if they are arranged in a random (2d from the looks of it) lattice... I mean, I can see it in my head, but not in their examples.
Am I missing how they are being placing the gyroscopes in a 3d lattice?
mackita
not rated yet Jan 15, 2018
They "placed" gyroscopes in 2D lattice, but these gyroscopes were "allowed" to precess and wobble in 3D and to transfer their precession to another neighboring gyroscopes in spin waves. Everything was virtual only indeed.
Whydening Gyre
not rated yet Jan 17, 2018
They "placed" gyroscopes in 2D lattice, but these gyroscopes were "allowed" to https://en.wikipe...ecession and wobble in 3D and to transfer their precession to another neighboring gyroscopes in spin waves. Everything was virtual only indeed.


Very limited 3d action, then. A narrow band layer.

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