Recent Publications

Quantitative reconstruction of atomic orbital densities of neon from partial cross sections

The approach of photoemission orbital tomography, i.e., the orbital density reconstruction from photoemission of planar molecular layers by using a formalism equivalent to a Fourier transformation, is transferred to free atoms. Absolute radial orbital densities of neon 1s, 2s, and 2p orbitals are reconstructed with a central-field one-electron model, using well-known atomic photoionization data. The model parameters are optimized by a Markov chain Monte Carlo method with Bayesian inference from which uncertainties for the reconstructed orbital densities are derived. The presented model opens the path for photoemission orbital tomography as a powerful tool, as well as for a quantitative analysis.

Phys. Rev. A 109, 012814 (2024)

Orbital-selective metal skin induced by alkali-metal-dosing Mott-insulating Ca2RuO4

Doped Mott insulators are the starting point for interesting physics such as high temperature superconductivity and quantum spin liquids. For multi-band Mott insulators, orbital selective ground states have been envisioned. However, orbital selective metals and Mott insulators have been difficult to realize experimentally. Here we demonstrate by photoemission spectroscopy how Ca2RuO4, upon alkali-metal surface doping, develops a single-band metal skin. Our dynamical mean field theory calculations reveal that homogeneous electron doping of Ca2RuO4 results in a multi-band metal. All together, our results provide evidence for an orbital-selective Mott insulator breakdown, which is unachievable via simple electron doping. Supported by a cluster model and cluster perturbation theory calculations, we demonstrate a type of skin metal-insulator transition induced by surface dopants that orbital-selectively hybridize with the bulk Mott state and in turn produce coherent in-gap states.

Commun Phys 6, 323 (2023)


Linear colossal magnetoresistance and magnetic textures in LaTiO3 thin films on SrTiO3

Linear magnetoresistance (LMR) is of particular interest for memory, electronics, and sensing applications, especially when it does not saturate over a wide range of magnetic fields. Structural disorder, however, also tends to limit the mobility and hence the overall LMR amplitude. An alternative route to achieve large LMR is via nonstructural inhomogeneities which do not affect the zero field mobility, like magnetic domains. Here, we report a colossal positive linear magnetoresistance in LaTiO3/SrTiO3 heterostructures, with amplitude up to 6500% at 9T at low temperature. The colossal amplitude of the LMR, one of the largest in oxide heterostructure, stems from the unusual combination of a very high heterostructure mobility, up to 40 000 cm2V1s1, and a very large coverage of low-mobility regions. Low-temperature Lorentz transmission electron microscopy measurements further reveals a striped magnetic structure at the sub-µm scale in the LaTiO3 layer ...

Phys. Rev B 108, 245405 (2023)


Research Groups

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.