Research Interests
Our research focusses on the spin properties in quantum materials and the influence of spin-orbit interaction (SOI) on the novel electronic properties of such materials. The main experimental techniques are different variations of angle-resolved photoemission spectroscopy (ARPES) and other spectroscopic methods. Over the last decades we have especially developed expertise in spin-resolved ARPES (SARPES) at synchrotrons and time-resolved techniques, such as tr-ARPES, at the LACUS facility at the EPFL.
The activities of the group are mainly experimental and curiosity driven and can be divided into three general subsections.
The first one focusses on the discovery of novel physical phases. This used to primarily concern how SOI can induce new material properties, with Rashba systems, topological insulators, and Weyl semimetals as famous examples. Recently we have expanded our activities to the interplay of real space spin arrangements and the crystal symmetry, leading to altermagnetic spin-order and the lifting of band degeneracy also in the absence of SOI or a net magnetisation.
The second topic is the manipulation of the spin order by external parameters as a first step towards spintronics, or spin-orbitronics devices. We have managed to control the Rashba-type spin splitting by chemical substitution, interface engineering, semiconductor doping, external electric fields, and optical excitation. Based on this experience we have also been able to manipulate the properties of multiferroic materials by similar means, including magnetisation switching by an electric field or by light.
The last subsection is the use of the spin signal in SARPES to explore the fundamental properties of matter and quantum mechanics in a more general sense. To a large extent this relies on the quantum interference of spin states, which provides phase sensitivity to our measurements. A prominent result has been the experimental measurement of the time scale associated with quantum transitions without using an external clock. This time is found to be in the order of tens to hundreds of attoseconds with a strong increase upon symmetry reduction. There are about as many attoseconds in a second, as that there are seconds in the age of the universe. To be able to grasp what happens on such ultrashort time scales, we have recently started to look at the role of time in quantum mechanics.
To extend our research possibilities we are constantly developing experimental techniques and their interpretation, such as new detection and sample environments and a thorough description of spin interference processes.