For the first time, physicists have captured an enigmatic state of matter on video.
Using a scanning transmission X-ray microscope, the research team has recorded the oscillations of a time crystal made out of magnons at room temperature. This, they said, is a significant breakthrough in the study of time crystals.
"We were able to show that such space-time crystals are much more robust and widespread than first thought," said physicist Pawel Gruszecki of the Adam Mickiewicz University in Poland.
"Our crystal condenses at room temperature and particles can interact with it - unlike in an isolated system. Moreover, it has reached a size that could be used to do something with this magnonic space-time crystal. This may result in many potential applications."
Time crystals, sometimes also referred to as space-time crystals, and only confirmed to actually exist a few years ago, are as fascinating as the name suggests. They are a lot like normal crystals, but for an additional property.
In regular crystals, the constituent atoms are arranged in a fixed, three-dimensional grid structure - think of the atomic lattice of a diamond or quartz crystal. These repeating lattices can differ in configuration, but within a given formation they don't move around very much: they only repeat spatially.
In time crystals, the atoms behave a bit differently. They oscillate, spinning first in one direction, and then the other. These oscillations - referred to as 'ticking' - are locked to a regular and particular frequency. So, where the structure of regular crystals repeats in space, in time crystals it repeats in space and time.
To study time crystals, scientists often use ultra-cold Bose-Einstein condensates of magnon quasiparticles. Magnons are not true particles, but consist of a collective excitation of the spin of electrons - like a wave that propagates through a lattice of spins.
The research team led by Gruszecki and his colleague, physics doctoral student Nick Träger of the Max Planck Institute for Intelligent Systems in Germany, did something different. They placed a strip of magnetic permalloy on an antenna through which they could send a radiofrequency current.
That current produced an oscillating magnetic field on the strip, with magnetic waves travelling onto it from both ends; these waves stimulated the magnons in the strip, and these moving magnons then condensed into a repeating pattern.
"We took the regularly recurring pattern of magnons in space and time, sent more magnons in, and they eventually scattered," Träger said. "Thus, we were able to show that the time crystal can interact with other quasiparticles. No one has yet been able to show this directly in an experiment, let alone in a video."
The video above shows the magnetic wave-front propagating through the strip, filmed at up to 40 billion frames per second using the MAXYMUS X-ray microscope at the BESSY II synchrotron radiation facility at Helmholtz Zentrum Berlin in Germany.
Time crystals should be stable and coherent over long time periods, because they - theoretically - oscillate at their lowest possible energy state. The team's research shows that driven magnonic time crystals can be easily manipulated, opening a new way to reconfigure time crystals. This could open up the state of matter for a range of practical applications.
"Classical crystals have a very broad field of applications," said physicist Joachim Gräfe of the Max Planck Institute for Intelligent Systems.
"Now, if crystals can interact not only in space but also in time, we add another dimension of possible applications. The potential for communication, radar or imaging technology is huge."
The research has been published in Physical Review Letters.