Group Leader Profiles

The research in our group is focused on the electronic and magnetic properties of few level systems looking for new quantum limits at the atomic scale. We are exploiting the interplay of magnetism, superconductivity, and correlation effects to isolate few level systems and understand their dynamics. Using scanning tunneling microscopy at lowest temperatures (between 10mK and 500mK), we study individual magnetic impurities coupled to superconducting substrates. We are interested in the resulting phenomena, such as Yu-Shiba-Rusinov states, and their suitability for quantum sensing or information processing. In addition, we combine electron spin resonance spectroscopy with scanning tunneling microscopy to understand and manipulate single spin systems isolated from their enviornment.

The understanding of fundamental, physical processes in quantum materials and the identification of universal aspects among them constitutes a necessary basis for the design of new quantum materials with desired functionalities. Our group investigates the collective behavior of interacting electrons which gives rise to the many fascinating phases of matter in quantum materials. We seek to explain the underlying mechanisms behind the phase formation and to determine characteristic properties of the different phases.We are particularly interested in situations when excitations of different phases strongly interact so that it is essential to consider their mutual influence on each other. This includes, for example, the study of quantum phase transitions or unconventional superconductivity. To account for the decisive role of interactions and the interplay of different degrees of freedom in these complex situations, we employ modern, field-theoretical tools with an emphasis on renormalization group techniques. We make use of microscopic and effective descriptions inspired by experimental observations to obtain a comprehensive picture of correlated phases in quantum materials.

Our group investigates correlated electron systems, i.e., materials where interactions between electrons are crucial if we want to understand their properties. We have a certain focus on numerical investigations of model systems: While models are of course a severe simplification of a material, this abstraction implies at the same time that we can use them to test our understanding of the dominant processes and to identify the most important aspects. Current focuses of our research are multi-orbital systems, e.g. iron-based superconductors or iridates, and topological states of matter that arise through electron-electron and electron-spin interactions.

Solid state physics, correlated electron systems, molecular quantum materials, magnetically frustrated systems, quantum spin liquids, topological materials, Dirac and Weyl electrons, physics of low-dimensional solids, superconductivity, materials for quantum computers, superconducting electronics, electrodynamics of solids, infrared and THz optical measurements of solids, microwave spectroscopy, magneto-optics, ellipsometry,

We are extending the coupled cluster theory, one of the most successful theories for ab-initio simulations of molecules, to study strongly correlated, extended and periodic molecular systems. We are developing novel coupled cluster approaches and embedding methodologies, and use automatic coding techniques to implement the new methods. These methods can be applied to various molecular or model systems, with strongly and weakly correlated electrons, to calculate ground and excited state properties and to predict or explain experimental findings.

Our interdisciplinary research group explores how to teach crystals tricks of living matter by investigating dynamic features of molecular framework materials such as metal-organic and covalent organic frameworks (MOFs and COFs). By specifically tuning the structural topology of the framework, we create soft porous crystals which exhibit pore contraction and/or expansion as a response to the adsorption of gases and fluids or external triggers such as light irradiation. Such materials can act as responsive cargo-release systems, nanoscopic sensors or feature counterintuitive phenomena such as negative gas adsorption. We furthermore construct frameworks which contain molecular machines such as light-driven molecular motors and switches as responsive and intrinsically dynamic building blocks. We aim towards collective operating molecular machines in the solid state which are able to actively transport molecules in the pore space and facilitate dynamic conversion and storage of energy carriers and other small molecules. Our diverse team uses a wide range of synthetic and experimental tools and collaborates in national and international research projects to push the boundaries of dynamic features in crystalline solids.

My research interests deal with the design, synthesis and characterization of novel liquid crystalline materials, hybrid materials of dyes and liquid crystals, as well as biomaterials. We try to understand structure property relationships in such materials towards novel organic electronics, ion conductors and battery materials.

The research in my group is mainly focused on non-equilibrium phenomena in Quantum Materials as well as on novel Josephson and Proximity effects using triplet superconductors. One major direction of our actual investigations are Higgs oscillations in superconductors under non-equilibrium conditions. Employing various non-equilibrium techniques we have predicted unique effects that provide novel insights into unconventional superconductors. We collaborate with many experimental groups in Stuttgart as well as in Toyko and Vancouver within the framwork on the Max Planck--UBC--UTokyo Center for Quantum Materials. With the prediction of novel and Josephson and Proximity effects in triplet junctions my group has opened a new field of research in condensed matter physics. Finally, I pioneered a new field 'Higgs spectroscopy' where collective modes of the superconducting order parameter classifies the ground state. A new field in the area of superconductivity. Experiments have confirmed our recent predictions.

The work focuses on synthesis and detailed characterization of metal-rich compounds, preferentially containing nitrogen as a constituent. First emphasis is the design and development of preparative techniques as basis for synthesis of novel materials. Special attention is granted to structural characterization, electronic and magnetic properties as well as mechanical and chemical behavior. These data are inevitable for any detailed consideration of chemical bonding and potential applications. • Advanced solid state synthesis of functional materials including various high pressure techniques, solvothermal synthesis and crystal growth, high temperature synthesis • Solid state reaction pathways and crystal growth mechanisms • Magnetic and superconducting materials, ionic conductors

Our research deals with the theoretical description of the emergent collective phenomena that arise in interacting quantum many-body systems, resulting from competing interactions, disorder, and topology. More specifically, we are interested in unconventional and topological superconductivity, complex phase diagrams, the impact of impurities in crystals, spin-orbit coupling, magnetism, spin liquids and topological order, moiré superlattice systems, non-Hermitian many-body physics, and more. To address these problems, we use a combination of analytical and numerical techniques of quantum field theory and statistical mechanics. Furthermore, we explore the potential of machine-learning to address problems of many-body physics.

Among the possible systems that exhibit quantum properties, molecular spin qubits (MSQs) are one of the most versatile platforms. At the heart of MSQs is the electronic spin, which can originate from unpaired electrons of organic centers, transition metals or lanthanides. The organic ligand surrounding the qubit can also be engineered to tune the electronic and spin properties. My group focuses on the deposition of MSQs on surfaces and investigation using spectroscopic techniques, in particular magnetic resonance. We also aim to extend the operating frequency range from X-band (9 GHz) to THz (> 100 GHz) using plasmonic metasurface magnetic resonators designed and fabricated by us. The group is therefore very multidisciplinary, at the interface of chemistry and physics, and young, having been established in January 2024