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 theory group has a long standing experience in the study of quantum phenomena in the field of atomic, molecular and optical physics. A special focus is on the man-body properties of strongly interacting quantum systems, as naturally realized with dipolar gases, cold atoms in optical lattices, polar molecules, and photons in a Rydberg media. The main research goals are the creation of exotic states of matter with ultra-cold gases, the design of quantum simulators for topological ordered phases and the study of their application for quantum information, as well as the understanding of strongly correlated states.

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 electrons, physics of low-dimensional solids, superconductivity, materials for quantum computers, electrodynamics of solids, infrared and THz optical measurements of solids, microwave spectroscopy, magneto-optics, ellipsometry, broad-band electron spin resonance

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 group works at the interface between nanophotonics and DNA nanotechnology. We aim for the realization of artificial nanofactories, in which DNA-based cellular mimics can be built and work in concert, in direct resemblance to the biological systems in living cells. Using bottom-up (DNA-origami) and top-down (electron beam lithography) nanotechniques we develop nanophotonic building blocks for biology, chemistry, and materials science with both tailored optical response and active functionality. The dynamic building blocks allow us quantitative and kinetic understanding of structural changes, biological processes and phase changes materials down to the single particle level.

In our interdisciplinary and international research team of polymer chemists, physical chemists and materials scientists we are developing functional and intelligent polymer materials and devices.

One of the main aims is to control and manipulate structure-property relationships of hierarchical architectures from the molecular via the nanoscopic to the macroscopic device level.

Functionalities include:

• redox-activity for electrochemical sensors and electrocatalysis
• optical and electronic properties for polymer (opto)electronics
• stimuli-responsive behavior applicable as intelligent skin for controlled drug release in pharmaceutical applications and as actuators and sensors for soft robotics applications

Quantum Control with hundreds of qubits is possible if neutral single atoms are trapped in arrays of optical tweezers or in optical lattices. Controlled interaction either via Rydberg excitation or magnetic interactions in optical lattices allow to setup strongly correlated quantums states. Singe atom optical readout via fluorescence allows to connect the qubits to a measurement apparatus without any electircal wiring. We are operating both quantum simulators and computers on these ideas. key words: Quantum Computing, Quantum Simulation, Atomic physics).

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.

Our research group studies electronic and magnetic structures of quantum materials. A special focus is on topological materials, which exhibit unusual properties, such as exotic surface states and anomalous transport phenomena, that are unaffected by continuous deformations, e.g., stretching, compressing, or twisting. Our aim is to develop a theoretical framework to describe these topological properties, and to find new ways how to use them in the laboratory and for device applications. We seek to classify topological materials in terms of symmetries and to discover new remarkable examples. Current research priorities focus on the topological properties of nodal-line semimetals, topological metals with nodal planes, quantum magnets, and unconventional superconductors, which we study using both analytical and numerical techniques.

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.

We focus on the spectroscopic and magnetic study of molecular nanomagnets. These materials have been proposed for applications in fields ranging from quantum computing to magnetic data storage. We are especially interested in understanding the transition from the microscopic quantum mechanical world of small particles to the macroscopic classical world that we live in. We specialize in advanced spectroscopic studies, including those based on electron spin resonance-related techniques, to investigate the magnetic anisotropy and quantum coherence and their origins.