Chirality in the kagome metal CsV₃Sb₅

Using x-ray photoelectron diffraction (XPD) and angle-resolved photoemission spectroscopy, we study photoemission intensity changes related to changes in the geometric and electronic structure in the kagome metal CsV3⁢Sb5 upon transition to an unconventional charge density wave (CDW) state. The XPD patterns reveal the presence of a chiral atomic structure in the CDW phase. Furthermore, using circularly polarized x-rays, we have found a pronounced nontrivial circular dichroism in the angular distribution of the valence band photoemission in the CDW phase, indicating a chirality of the electronic structure. This observation is consistent with the proposed orbital loop current order. ...

Phys. Rev. Lett. 134, 096401 (2025)

All-optical quality-control of indenene intercalation into graphene/SiC

Intercalating two-dimensional quantum materials beneath a sheet of graphene provides effective environmental protection and facilitates ex situ device fabrication. However, developing a functional device requires rapid, large-scale screening methods to evaluate the quality of the intercalant, which to date can be monitored only by slow, ultra-high vacuum-based surface science techniques. In this study, we utilize ex situ Raman micro-spectroscopy to optically and nondestructively identify the quantum spin Hall insulator indenene, a monolayer of indium sandwiched between a SiC(0001) substrate and a single sheet of graphene. ...

Appl. Phys. Lett. 125, 223102 (2024)

Epitaxial RuO₂ and IrO₂ films by pulsed laser depoition on TiO₂(110)

We present a systematic growth study of epitaxial RuO₂(110) and IrO₂(110) on TiO₂(110) substrates by pulsed laser deposition. We describe the main challenges encountered in the growth process, such as a deteriorating material flux due to laser-induced target metallization or the delicate balance of under- vs over-oxidation of the “stubborn” Ru and Ir metals. We identify growth temperatures and oxygen partial pressures of 700 K, 1 × 10⁻³ mbar for RuO₂ and 770 K, 5 × 10⁻⁴ mbar for IrO₂ to optimally balance between metal oxidation and particle mobility during nucleation. In contrast to IrO₂, RuO₂ exhibits layer-by-layer growth up to 5 unit cells if grown at high deposition rates. ...

APL Mater. 12, 101110 (2024)

Nanophysics at surfaces

The research activities of our group are concerned with the physics of low-dimensional systems, where the electron states resulting from dimensional confinement lead to unusual conduction properties and to phase transitions as a function of temperature.

Oxide interfaces

Our group focusses on the electronic structure of correlated systems in transition metal oxides (TMOs). Special interest lies in the interplay of different degrees of freedom (charge, spin, orbital, lattice) in the light of metal-insulator and other phase transitions.

Neutron and resonant X-ray spectroscopy

In our group we investigate complex, functional materials such as transition metal oxides, which are used in the emerging field of correlated nanoelectronics. Unlike with conventional semiconductors, exotic superconducting, orbital and magnetic states can be realized at the interfaces in layered structures comprising such materials.