Projects
The group is engaged in the investigation of anomalous properties of condensed matter systems as a consequence of strongly interacting electrons and spins.
Basically, our research aims at addressing the following questions: How do quantum objects (electrons or spins) behave when their motion is confined by the particles’ mutual interactions, so that the motion of an individual particle depends in a complex manner from the behavior of all others? What are the decisive ordering mechanisms which govern the collective behavior of the whole ensemble? What are the properties of such new forms of order?
These interactions, or correlations, may lead to surprising, often spectacular phenomena. Among others these include novel types of superconductivity or magnetic phases (magnets without order), the properties of which are rather reminiscent of liquids (spin liquids).
In order to understand these phenomena in detail, and to find new correlation phenomena, we expose the electron and spin systems to distinct, sometimes extreme conditions. Metal-organic solids have turned out to be particularly well-suited for this kind of research, as in these systems the interaction parameters can be tuned by physical (application of external pressure) or chemical (via substitution) means.
Our group is dealing with the following projects:
- Anomalous states (such as strange metals, multiferroics, unconventional superconductors) close to the Mott metal-insulator transition with particular attention paid to the role of antiferromagnetic order, frustrating magnetic interactions, dimensionality and the coupling to the lattice degrees of freedom.
- Interplay of superconductivity, magnetic and structural phase transitions in iron-pnictides.
- The collective behavior of strongly correlated electrons in novel materials, mainly molecular-based systems, with a high degree of tenability.
- Properties of low-dimensional quantum spin systems with special emphasis placed on the role of frustrating interactions; Properties of spin liquids and the behavior at magnetic field- or pressure-induced quantum critical points.
The materials of choice are compounds containing at least one organic or molecular component. On the metallic side, these are the so-called organic charge-transfer salts where a stable organic molecule (such as BEDT-TTF) is combined with a suitable inorganic acceptor complex.
For the quantum spin system, transition metal ions with incomplete d-shells or stable organic radicals are used as functional units. These magnetic building blocks are bridged by various, mainly organic linkers to form extended interacting magnetic systems. All systems share a high degree of flexibility enabling their properties to be tuned by variation of chemical and physical parameters.