Studying the extraordinary physical properties of so-called "Quantum Materials" and exploring their potential for novel functionalities are the main emphases of our research activities. These Quantum Materials are investigated using sophisticated synthesis techniques, a broad spectrum of state-of-the-art scientific instruments, as well as tailor-made high-end methods including highest resolution spectroscopy.
In Quantum Materials a possible potential for technological applications emerges from their complex, quantum mechanical electronic properties. These electronic properties may
- result from a complex interplay and ordering of electronic spin,
- orbital, charge and lattice degrees of freedom,
- emerge in a more general sense from the presence of strong electronic correlations,
- appear through competing or strongly frustrated magnetic interactions, or
- evolve in the context of topologically protected spin and charge states.
The above mentioned physical material's properties manifest in a number of material classes: in certain families of transition-metal oxides, in molecular solids and in a range of intermetallic materials. What sets these systems apart is that their valence and conduction electrons typically retain to some extent their atomic character, resulting in a rich interplay of localized and delocalized electronic degrees of freedom. This renders these materials both practically and conceptually very different from simple metals and semiconductors with well-understood itinerant quasi-particles. Often the quantum mechanical interplay between the localized and delocalized electronic degrees of freedom leads to anomalous charge transport properties, for instance due to the presence of metal-insulator transitions, and exceptional types of ordering phenomena, such as unconventional forms of superconductivity and quantum magnetism. Functionalities that arise from this are for instance large magnetocaloric effects, high temperature superconductivity, magnetism with very strong anisotropy and colossal/giant magnetoresistance.
Our research areas
Examples for our current research activities are
- unconventional superconductivity which is found at high application-relevant temperatures and magnetic fields,
- switchable metal-insulator transitions which may also cause technologically promising, extremely large magneto-resistances,
- magnetoelectric and spin-lattice couplings with application potential on magneto-electric data storage and magnetocaloric technology, respectively,
- dissipationless. i.e. ballistic spin transport of bulk or surface states,
- complex ordering phenomena of electronic degrees of freedom such as nematic order, orbital polarons, and superimposed (chiral) density waves, or
- unusual spatial spin structures such as the skyrmion lattices with their now frequently discussed potential for new magnetic data storage.
The plethora of spectacular and surprising phenomena that can occur in Quantum Materials poses one of the greatest set of challenges for cutting-edge experimental and theoretical condensed matter physics. As a rule material-specific predictions for the occurrence of many of these phenomena are very difficult, even if some of the presently booming research topics in this field, for instance the investigation of magnetic skyrmions and new topological states of matter, have emerged from a strong theoretical research effort and remain being strongly pushed by it.
“Nanometer-scale Quantum Materials”
When the dimensions of materials are restricted to the nanometer length-scale, new electronic properties emerge. This is related to the fact that any macroscopic object, when scaled down to a nanometer-scale, starts exhibiting distinct quantum mechanical properties. However, at the nanoscale also entirely new physical properties may emerge, for instance at surfaces and interfaces of topological insulators (TIs) where the spin of surface electrons is locked to their momentum, a property that is interesting in the context of spintronics.
The technological ability to engineer and shape materials at the nanoscale opens up a very well-defined road to control the materials properties and functionality in a systematic manner. It requires the synthesis, modelling and structuring of nanosystems, which is pursued in the context of a broad span of nanoparticles, ranging from endohedral fullerenes, carbon-based buckytubes to intermetallic or oxide nanoparticles. This combined approach is also the basis for the design of interfaces and heterostructures of superconducting materials, magnetic systems and molecular solids. In these heterostructures charge transfer effects at or across interfaces are decisive for the properties and functionality. An advantage of such interfaces is that they can be modified and engineered to a much greater extent than bulk Quantum Materials.
Building on the traditional strength in the field of Quantum Materials, and in order to strengthen in particular this research area and its potential for device applications, in 2013 the Center for Transport and Devices of Emergent Materials (CTD) has been founded together with the TU Dresden. In the CTD Quantum Materials will be experimentally investigated and theoretically modelled in the form or as a part of nanoscale electronic devices. This will allow studying their fundamental materials properties at the nanoscale, such as quantum interference, ballistic transport, spin dephasing, spin injection, interface and surface transport. Additionally, specific applied research will be bridged with materials synthesis together with the investigation of complex new matter and e.g. the materials challenges for nanotechnology in electronics on either side of the bridge.
Unique methodology: search, synthesis, analysis, and application potential of new materials
Our research teams search for new materials with the outlined unusual electronic properties and study their fundamental physical properties using a broad range of experimental techniques. Customized high resolution methodology is developed according to the specific scientific questions and phenomena, and finally, based on the experimental results, the chemistry, the morphology and the intrinsic physical properties of the materials are optimized with respect to technical applications. Some of the methodological developments of our institute push the limits of current condensed matter research. Such set-ups as well as the special infrastructure for materials synthesis are made available to cooperation partners at universities (crystal growth laboratory), worldwide users (ARPES measurement stations at the Berlin Synchrotron BESSY), or to industry partners (laboratory for spectroelectrochemistry).
Application-driven research activities
Based on our scientific expertise, our methodological experience, and based on our dedicated knowledge of specific materials classes, we also perform application-driven research in close cooperation with various industry partners. In many of these activities key challenges of the modern industrial and information society are addressed. For example, there are projects in cancer research based on our knowledge of molecular nanostructures. Additionally, our specific methodology and expertise for spectroelectrochemistry, magnetic materials, and oxide nanomaterials is used in industry projects concerning energy and/or mobility. The activities on novel magnetic materials are also motivated by the urgent issues of resources and sustainability. Moreover, the industry-oriented research of our institute includes since many years the topic "Surface Acoustic Waves (SAW)" dealing with innovative micro-acoustic components and devices as well as the associated high-tech materials and technologies. The recently founded "SAWLab Saxony - Competence Center for Acoustoelectronic Phenomena, Technologies and Devices" aims to bundle our profound SAW knowledge with experience and demands of several small and medium-sized Saxon high-tech companies fostering the close cooperation of our institute with the regional industry.