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 research in our group focuses on the study of transition-metal oxide thin films and multilayers using resonant x-ray spectroscopy. Our goal is to combine different quantum materials in a heterostructure to stabilize new phases with functional properties that can be used, for example, in sensor, memory or logic applications.

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.

Polarized x-ray based studies on magnetism and modern magnetic materials utilizing X-ray magnetism circular dichroism (XMCD) and related techniques, like X-ray resonant reflectivity (XRMR), and X-ray spectroscopic microscopy. While beeing focused on Keimer Department research topics, related phenomena are interface magnetism, spin-orbit-coupling and spin-orbit-torque, voltage induced magnetocrystalline anisotropy, orbital moments, nano-magnetism, spin conduction and relaxation, and interfacial exchange interaction.

The department uses neutron and X-ray diffraction and spectroscopy as well as optical spectroscopy and Raman scattering to explore the structure and dynamics of materials with strong electron correlations. We also have a strong effort in the development of new spectroscopic methods. As the close collaboration between experimentalists and theorists is essential for progress in this field, a small theory group operates within the department.

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.

Our research explores the rational synthesis of new functional materials by combining the tools of molecular, solid-state and nanochemistry. Research interests include the design of organic, inorganic and hybrid materials for solar energy conversion and storage, ion conductors for electrochemical energy storage, and “smart” photonic crystals for optical sensing. We aim at creating function from both atomic-scale structure and nanoscale morphology, with a strong emphasis on exploring structure-property relationships based on a variety of diffraction and spectroscopic techniques. Recent activities include the development of molecular frameworks for solar batteries, “dark” photocatalysis, photomemristive sensors, and (photo)electrocatalytic CO2 conversion, the development of quantum materials for (photo)electrocatalysis, as well as the design of lithium and sodium thiophosphate and sulfide solid electrolytes for all-solid-state batteries. Dr Simon Krause, Group Leader in the Nanochemsitry Department offers a PhD position on the investigation of light-driven molecular machines in dynamic framework materials for energy conversion and catalysis.

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

Electrochemistry provides us with an unmatched lever to control the chemical equilibrium. Employing this lever in inorganic solid state chemistry allows the access to new (metastable) phases and structures. Concomitantly, electrochemistry affords an outstanding precision in the control and analysis of the composition of phases. This is particularly needed when studying complex physical phenomena such as superconductivity, because these properties are often very sensitive towards composition.
My group follows a combined electrochemical and solid state chemical approach, where electrochemistry is used to change the composition of solids post-synthetically, or compounds are synthesised directly from solution. Joining this approach with in-situ X-ray diffraction finally establishes a direct link between the electrochemical experiment and structural changes. This not only provides insights into complex physical phenomena, but is also the foundation of more applied topics such as battery research and electrochemical sensing.

Our team concentrates on the nanoanalysis of interreactions. We are experts in atom probe tomography to investigate solid-state processes in single-atom sensitivity and resolution. Presently, innovative instruments are developed to study the chemistry of solid/liquid interfaces with the same methods. From the perspective of materials physics, short-circuit atomic transport along triple junctions or other higher order defects in complex materials are of particular interest. We are running a sputter deposition laboratory to produce required model structures from metallic thin films and metallic nanowires. We assemble promising all-solid-state batteries and sensor devices. Theoretical work is performed by Molecular Dynamics or Monte-Carlo simulation to predict field evaporation and emission from nanometric tips. Furthermore, we study thermodynamic properties of topologically necessary defects and the mechanical stability of thin films by theoretical methods.

In our group we study the atomic and electronic structure of solid surfaces and 2D materials. A strong focus of the research is the growth and functionalization of epitaxial graphene on Silicon Carbide. By means of atomic intercalation we can tailor graphene’s electronic properties. We use angle-resolved photoemission spectroscopy (ARPES) to investigate doping and renormalization of the π-bands in graphene – in the home lab and at synchrotron facilities. Structured SiC substrates are the basis to grow epitaxial graphene nanoribbons with a one-dimensional electronic spectrum. The interaction of hetero-epitaxial 2D materials (e.g. transition metal dichalcogenides) and molecular layers with the graphene and its influence on both, the graphene and the 2D layer is studied with a multitude of surface science methods in ultra-high vacuum.

The Stuttgart Center for Electron Microscopy (StEM) is an internationally recognized center for advanced electron microscopy. The center has a long tradition of applying and developing new microscopy techniques for the investigation of novel materials. The extensive expertise of the researchers and technicians in the group is complemented by a range of instruments; StEM possesses 8 TEMs, including two state-of-the-art Cs-corrected TEMs, 5 SEMs, and a suite of specialized sample preparation equipment. The group undertakes both independent research and collaborative projects with other groups at the Stuttgart Max Planck Institutes. In heterostructures and functional thin films, StEM investigates structure and chemistry around defects and interfaces at atomic resolution. In bio-composite systems, StEM is studying biologically-driven mechanisms for nanostructure replication and organization. The group has a well-developed program investigating plasmons and electron-interactions, both through experiments and modeling. Many other research projects are described on the StEM webpages.