Jan 16 2018
According to University of Chicago scientists, individuals need not be perfectly organized to pull off a wave.
UChicago scientists crafted a structure that displays unusual waves--which can even be directed into particular shapes. (Image credit: Noah Mitchell/University of Chicago)
Physicists succeeded in exploring the behavior of a material whose structure is randomly arranged by using a set of gyroscopes linked together instead of using an orderly lattice. They discovered the possibility of setting off one-way ripples around the edges, a lot like spectators in a sports arena - a "topological wave," characteristic of a predominantly unusual state of matter.
Featured in the Jan 15th edition of Nature Physics, the discovery offers new insight into the physics of collective motion and could one day have implications for optics, electronics or other technologies.
The team, headed by Assoc. Prof. William Irvine, employed gyroscopes - the top-like toys used for playing by kids - as a model system in order to explore physics. Since gyroscopes move in three dimensions, if one connects them with springs and the spins them with motors, it will then be possible to observe all kinds of things about the rules that administer how objects move together.
Two years ago, the team observed a strange behavior in their gyroscopes: at specific frequencies, they were able to set off a wave that moved around the edges of the material in just one direction. This was considered to be odd, but had some counterparts in various other branches of physics. It is a behavior characteristic of a recently discovered state of matter known as a topological insulator.
As the next time, they tried to find which conditions were actually necessary, and while doing this they altered the pattern of the gyroscopes. Irvine and team scattered the points randomly around the place where the gyroscopes earlier had been neatly lined up in rows equally spaced, just like the lattice pattern in a crystal.
The gyroscopes were turned on, and they still continued to see the waves.
This is exceptionally strange. Conventionally, the lattice order is extremely important in physical properties. It is a bit like if every time a handful of puzzle pieces was tossed on the table, it still produced 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. 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.
Associate Professor William Irvine
A collective behavior with local roots is also really interesting because that's a much easier way to manufacture a material. It was thought spatial order had to be globally coordinated, but the fact that local properties are sufficient could open a lot of possibilities.
Noah Mitchell, First Author
There are a number of materials in the everyday world that do not have a crystalline structure, including Styrofoam, foam, plastic, glass and rubber. The physics behind these systems is yet to be fully understood than their crystalline counterparts, but as scientists’ potential to engineer them - including as metamaterials and quantum systems - grows, they are of growing interest. If these amorphous materials were capable of displaying some of the properties of crystals, it could set forth the foundations for new technologies.
Other coauthors included UChicago graduate student Lisa Nash and postdoctoral student Daniel Hexner, as well as Israel Institute of Technology professor Ari Turner.