Is anyone old enough to remember the ad in which two people walking down the street while snacking accidently bump into each other and discover peanut butter on a chocolate bar? Well, it turns out that when physics students run into each other on the street, the result is a quasicrystal with topological properties.
The students in question were members of two different labs in two different physics departments who were both out for a stroll on the same street in Tel Aviv – far from Rehovot and the Weizmann Institute. One was experimenting with a new kind of quasicrystalline optical system – thin optical fibers etched into glass that are arranged in quasicrystal fashion – ordered but non-periodic. The other was investigating a new class of materials called topological materials, in which the interior of the material is insulating but the surface conducts electricity. Some “shop talk” on their day off led them to realize that combining the two might help probe some unanswered questions.
These two were joined by another three students from the two departments, and the five embarked on an independent experiment. They created an optical quasicrystal and shined laser light through one optic fiber at a time. When light was shone through a middle fiber, it “hopped” across to the other fibers and exited through all of them. But if they passed the light through a fiber on just one of the edges, that light stayed on its edge without moving to the other fibers.
Even more wonderful and astonishing was the “adiabatic pump” they created. By varying the distances between one fiber and its neighbor along their lengths, they managed to get the beam of light to enter from one side and hop across the crystal, exiting from the opposite corner.
The explanation for this verges, to the uninitiated at least, on the magical: Those one-dimensional quasicrystals (the optic fibers) are a projection of a higher-dimensional system, and they preserve some of its properties. That means that if the same phenomenon can be found in two or three dimensions, these could be projections from systems of up to six dimensions.