A chiral topological material with unknown electronic properties

An international investigation has discovered a topological material endowed with chirality, the property that objects have of not being superimposable with their mirror image The topological materials gained notoriety upon receiving the Nobel Prize in Physics in 2016. Although the best known are the topological insulators – insulators inside and drivers on their surface – recently there has been a boom and physicists from all over the world work predicting and discovering new classes of these materials with unique electronic properties.

In this context, scientists from the Donostia International Physics Center (DIPC), the Paul Scherrer Institute in Zurich (Switzerland), the University of Oxford (United Kingdom), the Max Planck Institute (Germany) and the University of Illinois at Urbana-Champaign ( USA) have experimentally demonstrated the existence of chiral topological materials. The preview is published this week in the journal Nature Physics.

Chirality is the property of an object not to be superimposable with its mirror image, a phenomenon very widespread in nature. We can see it, for example, in the hands: the left does not adopt the same shape as the right, although we will turn it in different directions. It is only achieved if we invest it with the help of a mirror. Transferring this concept to the materials, means that in some crystals the imaginary spiral formed by its atoms rotates in a clockwise direction invariably and in others against. The chiral materials are very interesting because they can harbor ‘rare’ and unknown physical phenomena.

This study shows that a special chiral aluminum and platinum (PtAl) crystal has very unique properties at the electronic level. These are new fermions or pseudo-particles whose existence was predicted in 1941 and the two Ikerbasque researchers of the DIPC who participated in the study, Maia García-Vergniory and Fernando de Juan, already a couple of years ago. His works allowed predicting and theoretically classifying hundreds of new topological materials based on their symmetry. The experiments have been carried out in Oxford with a cubic sample of half a centimeter wide and metallic silver-white appearance. The glass was produced using a process that is reproducible only in a few laboratories worldwide.

In the cells of this crystal, which are repeated symmetrically, the individual atoms are arranged in the form of a spiral staircase. This results in new electronic behavior properties for the crystal as a whole.

N. B. M. Schröter, D. Pei, M. G. Vergniory, Y. Sun, K. Manna, F. de Juan, J. A. Krieger, V. Süss, M. Schmidt, P. Dudin, B. Bradlyn, T. K. Kim, T. Schmitt, C. Cacho, C. Felser, V. N. Strocov, and Y. Chen. “Chiral topological semimetal with multifold band crossings and long Fermi arcs”. Nature Physics 6 May 2019 (online). DOI: 10.1038/s41567-019-0511-y

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