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O: Fachverband Oberflächenphysik

O 101: Ertl Young Investigator Award Competition

O 101.5: Vortrag

Donnerstag, 19. März 2020, 12:30–13:00, TRE Ma

Discovery of chiral topological semimetals with multifold fermions and maximal Chern numbers — •Niels Schröter — Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland

Chiral topological semimetals (which possess neither mirror nor inversion symmetries) are expected host numerous novel phenomena, such as multifold fermions with large topological charge, long Fermi-arc surface states, unusual magnetotransport and lattice dynamics, and a quantized response to circularly polarized light - the first quantized response in metals. Until recently, all experimentally confirmed topological semimetals crystallized in space groups that contain mirror operations, which means that the aforementioned phenomena cannot appear.

Here I will present the first experimental evidence that AlPt and PdGa are chiral topological semimetals. Using angle-resolved photoelectron spectroscopy and ab-initio calculations, we show that these compounds host multifold fermions that carry the maximal Chern number that can be realized for linear band crossings in any material, which imposes an upper limit to the magnitude of many topological phenomena. Furthermore, by comparing two enantiomers (crystals with mirrored structure that do not coincide), we observe a reversal of their Fermi-arc velocities, which demonstrates that the handedness of chiral crystals can be used as a tuning parameter to manipulate the sign of their Chern numbers. I will furthermore demonstrate how time-reversal symmetry breaking can create novel topological multifold fermions that are elusive in non-magnetic compounds.