Laser “honeycombs” have enabled the simulation of theoretical materials with curious properties. By aligning multiple laser beams in such a way that they create standing waves with a hexagonal pattern, a team from ETH Zurich’s Institute for Quantum Electronics was able to trap a group of potassium atoms cooled to near absolute zero inside a vacuum chamber. The potassium atoms demonstrated behavior similar to that of electrons in graphene. “We work with atoms in laser beams because it provides us with a system that can be controlled better and observed more easily than the material itself,” said Gregor Jotzu, a physics doctoral student at ETH Zurich. When the system is shaken in a circular motion by placing vibrating piezoelectric crystals on mirrors that reflected the laser light, “the particles experience a twisted world,” said professor Dr. Tilman Esslinger. A Mobius strip can’t be transformed into a normal strip without cutting, making the two shapes topologically different. Courtesy of Gregor Jotzu/ETH Zurich. In this state the system has a different topology than ordinary materials, where time-reversal and inversion symmetry are broken. The concept of such topologically altered materials was proposed in 1988 by Princeton University physics professor Dr. Duncan Haldane The Zurich researchers stressed that their experimental work has not produced any new materials. “We just tested a concept,” Esslinger said. The work has, however, allowed the researchers “to investigate the properties of materials that don’t even exist yet,” Jotzu said. As the work is ongoing, the potential transfer of the experiments’ results to real materials remains uncertain. The researchers and other colleagues have considered that if circularly-polarized light could be sent on to real graphene, it may have a similar effect as shaking artificial graphene in a circular motion. The phenomenon could enable development of insulators that become conductors — and conductors that become insulators — when exposed to light. This could lead to a number of different electronic applications with extremely fast reaction times. The research was published in Nature (doi: 10.1038/nature13915). For more information, visit www.ethz.ch.