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
Tom van Waas (middle) with the other prize winners © 2022 Swiss Physical Society

Tom van Waas wins SPS best poster award

— At the 2022 SPS meeting, held in Fribourg from 27 – 30 June, Tom van Waas has won one of the three best poster awards for the work started as a MaNEP internship student in our group. The title of the poster is "Bayesian inference on electron-boson interaction from ARPES self-energies" and deals with an efficient method to extract the self-energies and Eliashberg function from high resolution angle-resolved photoemission spectroscopy (ARPES) data.

© 2022 EPFL

The first 10 PhD students selected in the 100 PhDs programme!

— The joint EPFL-UM6P initiative "Excellence in Africa" has now released the names of the first 10 students selected after the 1st call for proposals of the 100 PhDs for Africa programme.

Electronic structure of clean (left) and oxidised (right) InAs(111)© G. Aeppli 2022 EPFL

Towards compact quantum computers, thanks to topology

— Researchers at EPFL and PSI have compared the electron distribution below the oxide layer of two semiconductors. The investigation is part of an effort to develop particularly stable quantum bits –and thus, in turn, particularly efficient quantum computers. They have now published their latest research, which is supported in part by Microsoft, in the scientific journal Advanced Quantum Technologies.

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.

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