'Topological materials' produce electron states that can be very interesting for technical applications, but it is extremely difficult to identify these materials and their associated electronic states.
A 'crystal' made of light waves can now be used to deliberately drive the system out of equilibrium. By switching between simple and complicated states, the system reveals whether or not it has topologically interesting states.
TU Wien (Vienna) and several research groups from China have now developed new ideas and implemented them in an experiment. A "crystal " made of light waves is created to hold atoms in a very special geometric pattern. These "light crystals," which have been used in different ways for the manipulation of atoms, can now be used to deliberately drive the system out of equilibrium. By switching between simple and complicated states, the system reveals whether or not it has topologically interesting states. These findings have now been published in the journal Physical Review Letters.
The importance of topology can easily be seen if we pack too many things into a shopping bag: a bread roll may be slightly crushed and squeezed into a shape similar to a banana. Bread rolls and bananas have the same basic geometric structure, topologically they are the same. On the other hand, a donut has a hole in the middle, its topology is different. Even if it is slightly squeezed, its shape can still be easily distinguished from that of the bread roll.
With the help of interfering light waves, atoms can be held in pre-defined places, creating a regular grid of atoms, similar to a crystal, the atoms taking the roles of the electrons in a solid state crystal. By changing the light, the geometry of the atomic arrangement can be switched, in order to examine how the electron states would behave in a real solid state material.
This is an important new insight for research on topological materials. One could even adapt the artificial light crystals to simulate certain crystal structures and in order to find new topological materials.