Laboratory for Topological Matter

Topology at Bad Ragartz 2009
(Linea del Tempo continuo · Silvio Santini)

In the Laboratory for Topological Matter we study the influence of topology on the electronic structure, magnetic properties, and phase transitions. The studies systems include, among others, various types of topological insulators, Dirac, Weyl and related semimetals, skyrmions, transition metal oxides, and multiferroic materials. The topological properties are investigated using a variety of photon-based spectroscopic techniques such as ARPES and RIXS both at the Swiss Light Source of the Paul Scherrer Institute and at the LACUS laser facility at the EPFL. Special attention is paid to the reciprocal space spin textures of materials and the possibility to actively influence these.

Fermi surface of the TI PbBi4Te7 with spin texture and spindle torus Fermi surface of BiTeI
Theoretical and experimental observation of the unpaired Weyl points © 2021 PSI

Unpaired Weyl Point observed for the first time in crystalline solid

— It is widely believed that the appearance of Weyl fermions in solids is restricted by the well-known Nielsen-Ninomiya no-go theorem proposed during the 1980s, which states that zero dimensional (0D) Weyl nodes in topological semimetals should always appear in pairs with opposite chiral charges in 3D momentum space. As a consequence, the projections of the Weyl nodes on the surface Brillouin zone are always connected by Fermi arcs. Considerable theoretical efforts have been dedicated to search for unpaired Weyl fermions beyond this no-go theorem, as such a discovery would carry major fundamental implications. 

Credit: Hugo Dil (EPFL)

Observation of triple-point Fermions

— An international study, led by EPFL, has discovered a material that gives rise to rare, “triple-point” Fermions. The researchers have been able, for the first time, to identify the spins associated with them.

Profs. Lutherbacher and Boyarkine, Dil and Drabbels

Promotion at SB of one Associate and three Adjunct Professors

— At its meeting of 3-4 March 2021, the ETH Board has promoted Jeremy Luterbacher to Associate Professor and awarded the title of Adjunct Professor to three researchers of the School of Basic Sciences (SB). 

Dispersion of a TI and Rashba-Zeeman system © H. Dil 2020 EPFL

A single helix for novel quantum phenomena

— By growing thin films of SrTiO3 on thick wafers of the same material, researchers from the EPFL and PSI have been able to create a 2D electron gas that shows just one single spin component at the Fermi surface.

Crystal structures with opposite chirality © Schröter 2020 PSI

Cherned up to the maximum

— In topological materials, electrons can display behaviour that is fundamentally different from that in ‘conventional’ matter, and the magnitude of many such ‘exotic’ phenomena is directly proportional to an entity known as the Chern number. New experiments establish for the first time that the theoretically predicted maximum Chern number can be reached — and controlled — in a real material.

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