In order to express physical theories, science uses mathematical terms. So, the whole world can be described by equations - that´s about all physicists agree. For more than a hundred years, so-called Hermitian equations (named after Charles Hermite) have been used for. The French physicist had defined a certain property, which applies to all stable systems with measurable energy. In 1998, however, the American physicist Carl Bender published a theory that revolutionized this way of thinking. Bender argued that even systems without this Hermitian property can have measurable energies if they have an additional symmetry, namely when they are mirrored in space and time. These systems are called PT-symmetric - P for parity, T for time. For several years now, scientists have been trying to find out about these PT-symmetrical systems and apply them to all areas of physics.

Physicists at the research group "Diamond-/Carbon- Optics" (Prof. Alexander Szameit) have come a huge step closer to understanding the importance of these systems. They have found that so-called topological surface conditions can also exist in PT-symmetrical systems and reported in the specialist magazine "Nature Materials".

"Mathematics describe and classify bodies in rule quite abstract", explains Prof. Dr. Alexander Szameit the term topology. "Concentrating on the geometrical structure and the surface structure surprising coincidences can be found: for example, a CD is about the same as a cup with handles - both have one hole. This area of mathematics is called topology." Physicists also use this kind of description. Thus, certain physical properties of a system can be influenced in a completely new way by means of topological principles. Within the optics, for example, they are able to direct light completely around corners and edges without interference. Whether this method can be used not only for Hermitian, but also for PT-symmetrical systems has been controversial.

However for the first time, Szameits colleague and Ph.D. Steffen Weimann, has developed and implemented an experimental system in which such a topological approach also works for PT-symmetrical systems. "These systems extend our understanding of fundamental theories and thus opens up entirely new perspectives for the direction of light," says Steffen Weimann. In the long term, these new findings will enable us to develop entirely new materials in basic research.

Since Alexander Szameit took the leap from the junior professorship to the Chair for Experimental Solid State Optics at the University of Rostock, he and his colleague Steffen Weimann will continue their joint work at the new location.

PhD-Student is the first author of the article in which it is shown that so-called topological surface conditions can also exsit in PT-symmetrical systems . [J. Kasper, FSU] |

S. Weimann et al.: Topologically protected bound states in photonic parity-time-symmetric crystals; Nature Materials; DOI: 10.1038/NMAT4811

Steffen Weimann

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german version of the article >>> here

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