This Minerva research group focuses on the experimental studies of strongly correlated transition metal oxide thin films, multilayers, and superlattices. We use x-ray absorption spectroscopy and scattering to investigate the structural, magnetic, orbital and charge order in ultrathin layers. In particular our research concentrates on ordering phenomena occurring at interfaces in nickel oxide superlattices with composition RNiO₃−RXO₃ (R: rare earth ion and X: Al, Sc, Ga) and in heterostructures of Mott-insulating RVO₃. Using the advanced x-ray reflectivity analysis tool ReMagX we developed the new method of orbital reflectometry to study spatially resolved orbital polarization profiles in adjacent atomic layers of oxide superlattices. We collaborate closely with other groups in Keimer's department, the Technology Service Group as well as with external groups at the Helmholz-Zentrum Berlin and within the TransRegio TRR80.

The Max Planck Research Group "Electronic Structure of Correlated Materials" is focused on the computation of ground state and spectroscopic features for correlated materials with a combination of density functional methods and quantum many body theory. Specifically we concentrate on the electronic structure of surfaces or interfaces of correlated heterostructures. Condensed matter spectroscopy for correlated compounds provides clear evidence that for these materials the independent electron approximation fails in order to describe even low energy excitations in the system. Some of these materials are closer to the atomic limit than to a slightly disturbed free electron gas and we have to tackle the many-body Schrödinger equation with other means than the effective single particle strategy. While calculations of correlated materials are therefore extremely hard, it turns out that, on the other hand their phase diagrams are diverse and full of exotic and fascinating physics interesting for fundamental theory and possible technological applications at the same time. In the last decade a part of the experimental community has started to work on correlated systems which can be 'artificially' constructed on an atomic level. Our goal is to provide theoretical support for interpretation of experiments and, even more importantly, for exploring novel materials. Our tools include the merger of density functional theory (DFT) with many body methods like dynamical mean field theory (DMFT) and extensions like extended DMFT (EDMFT) or even GW+EDMFT as well as configuration interaction (CI) cluster calculations for certain spectroscopies. Parameter free calculations are possible with calculation of screened Coulomb potentials by constrained random phase approximation (cRPA) which guide us to a realistic low energy effective Hamiltonian of a given material. [more]

The "Ultrafast Solid State Spectroscopy" group is a joint Research Group of the Max Planck Institute for Solid State Research and the Department of Physics at the University of Stuttgart. The research interest is ultrafast spectroscopy of strongly correlated electron materials, and novel quantum materials. The group applies advanced nonlinear optical methods such as ultra-broad band pump-probe spectroscopy, not only to investigate ultrafast dynamics in complex solid-state materials, but also to control them with light. Combining these methods with high-resolution optical near-field microscopy we can access such dynamics even with sub-wavelength resolution down to the nanoscale. One research focus is the light induced superconductivity in high-temperature superconductors. We investigate different scenarios like the balancing between competing phases triggered by ultrashort light pulses or explore possibilities of dynamical stabilization in periodically driven light fields. The latter relates directly to another main research field of the group − quantum many body dynamics in correlated electron materials. We use advanced quantum materials, e.g. organic conductors and superconductors, as model systems to investigate the ultrafast dynamics of electronic correlations and their coupling to external excitations. We aim tracing the dynamics of the system directly on the time-scale of the effective electronic interactions. In order to control such systems we use mode selective driving of local (molecular) vibrations that allows us modulating the effective interactions and induce quantum quenches in solid state Mott systems. [more]

Research in the Organic Electronics Group focuses on novel functional organic materials and on the manufacturing and characterization of organic and nanoscale electronic devices, such as high-performance organic thin-film transistors, carbon-nanotube field-effect transistors, inorganic semiconductor nanowire field-effect transistors, and organic/inorganic hybrid radial superlattices. Of particular interest is the use of organic self-assembled monolayers in functional electronic devices. We are developing materials and manufacturing techniques that allow the use of high-quality self-assembled monolayers as the gate dielectric in low-voltage organic and inorganic field-effect transistors and low-power integrated circuits on flexible substrates. We are also studying the use of self-assembled monolayers for the preparation of nanoscale organic/inorganic superlattices that exhibit unique electrical, optical, and mechanical properties. Scientific work in organic electronics is highly interdisciplinary and involves the design, synthesis and processing of functional organic and inorganic materials, the development of advanced micro- and nanofabrication techniques, device and circuit design, and materials and device characterization. [more]

Research in the Solid State Nanophysics Group focuses on the study of the many unusual ways in which electrons organize themselves as a result of interactions and correlations among their charge and spin degrees of freedom, when these electrons are confined in one or more dimensions on the nanometer scale. Transport and optical properties are investigated with local probe methods, at low temperatures, in high magnetic fields, under high frequency radiation or any combination thereof. The electrons are confined either in III–V semiconductor heterostructures or in strictly two-dimensional crystals such as graphene, molybdenum disulfide or other single layers of the large class of layered materials with weak interlayer forces. Also hybrid stacks of these two-dimensional crystals, so-called van der Waals heterostructures, are fabricated and explored in a quest for novel functionalities and interaction physics. [more]