Atomic Physics: Laser Spectroscopy (Group Weis) (FRAP)
The research interests of the Fribourg group for Atomic Physics (FRAP) focus on the use of spin coherent atomic ensembles in fundamental and applied physics. Spin coherent atomic ensembles are highly sensitive probes for the study of a great variety of weak or strongly suppressed processes. The experimental techniques involve magnetic resonance and level-crossing spectroscopy of optically pumped alkali atoms. Investigated samples range from (coated and uncoated) vapor cells, intense thermal and laser-cooled beams to atoms trapped in crystalline helium matrices.
Atomic Physics: X-Ray Spectroscopy (Group Dousse) (AXP)
The potential of atomic inner-shell processes as a probe of atomic structure and dynamics, as well as in applied research is well established. Photon-atom and charged particle-atom interactions continue to play an essential role in the field of modern atomic physics. High-resolution x-ray spectroscopy permits to explore the many aspects of atomic excitation and decay channels. It represents a powerful and sometimes unique experimental technique. The development of x-ray synchrotron facilities, heavy-ion storage rings and numerous x-ray based applications has given a boost to the domain.
The research interest of the AXP group is focused on the photon and charged particle interactions with the inner-shells of atoms. The experimental technique consists to measure by means of high-resolution crystal spectroscopy the fluorescence x-rays from the irradiated solid, powdered, liquid and gaseous samples. Fundamental aspects of atomic excitation and decay processes resulting from collisions with photons, electrons, light charged particles and heavy ions as well as the dynamics of the investigated processes are of interest.
A further part of our activities is devoted to the metrology of x-ray transitions. In this case, the energies and natural widths of atomic core levels as well as the energies, linewidths and relative intensities of forbidden or exotic radiative transitions are investigated. The experimental methods and techniques developed within our fundamental research projects are also employed for various applications in materials sciences. The novel high-resolution grazing emission x-ray fluorescence (GEXRF) technique is a typical example of such spin-off results of our fundamental research.
Solid State Physics: Electron Spectroscopy (Group Aebi) (ES)
Our research is directed towards developing a better understanding of the peculiar physical properties of materials with strongly correlated charge carriers. In particular, we are investigating the electronic and magnetic properties of oxides, like the cuprate high T c superconductors (HTSC) or the layered cobaltate compound NaxCoO2 which becomes superconducting upon intercalation of water. We are also actively working on multilayers and heterostructures that combine the cuprate HTSC with metallic ferromagnets, like the manganites with their well known collosal magnetoresistance (CMR) effect or the ruthenate SrRuO3. We are also interested in the measuring and understanding the metamagnetic transition in Sr3Ru2O7 at 8T, a new class of quantum criticality, as well as understanding the charge carrier transport and spin diffusion in organic semiconductor/magnetic spin valve structures. However, our emphasis is on the competition between superconductivity and ferromagnetism and the investigation of subsequent new spin- and quantum phenomena.
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Solid State Physics: Magnetism and Superconductivity (Group Bernhard) (MS)
Our research is directed towards developing a better understanding of the unusual electronic and magnetic properties of transition metal oxides with strongly correlated electrons. Prominent examples are the cuprate high-Tc superconductors and the recently discovered iron arsenide superconductors. We also grow and investigate various kinds of oxide-based thin films, superlattices, and heterostructures. The interfaces of these artificial materials can be grown with atomic precision. This allows us to combine materials with different order parameters and interactions and to control their proximity coupling as to achieve artificial materials with improved or novel properties and functionalities. One example is the combination of cuprate high-Tc superconductors and ferromagnetic manganites, which are well known due to their collosal magnetoresistance (CMR) effect. Here we investigate the competition between superconductivity and ferromagnetism and search for new spin- and quantum phenomena. Another example concerns the confined high mobility electron gas which develops at the interface between a LaAlO3 thin film and a SrTiO3 substrate. Last but not least some of us are also actively working on organic materials and thin films with the emphasis on their properties for application in spintronics.
Soft Matter and Photonics (Group Scheffold) (SMP)
"Soft Condensed Matter" is a rapidly expanding field of research, in which one primarily focuses on three different complementary areas, i.e., the study of the properties of colloids, polymers and surfactants (e.g., micelles and microemulsions). A major goal is to understand the formation processes, structure, and functional properties of supramolecular systems that play an important role in real life. As it's title implies, it is the study of materials which are soft, i.e. easily deformable by external stresses or even thermal fluctuations. Soft condensed matter science is not only an attractive area of modern basic research, but is of considerable technological importance in areas such as, for example, the manufacturing of synthetic dispersions for coatings, ceramics fabrication, polymer processing, corrosion phenomena, environmental pollution, food technology, pharmaceutical industry, biocompatible materials, and biotechnology. Colloidal interactions are omnipresent and influence a large variety of technological processes, yet they are frequently invisible, often ignored and consequently ill-controlled.
Theory of Cold Atoms (Group Gritsev) (TCA)
Various systems of ultracold atoms in reduced dimensions provide a unique laboratory for studying effects of strong correlations and to address many interesting questions of nonequilibrium dynamics. Recent progress in quantum optics allows nowadays to create and to probe many-body strongly correlated states of light. New striking effects are expected to occur at the interface of the two fields. Therefore effects of strong correlations in systems of cold atoms and quantum optics are the main fields of my current research. I am using the whole spectrum of theoretical tools including various nonperturbative methods to study interesting new fundamental problems from these fields while keeping a close contact with experimental groups.
Theory of Condensed Matter (Group Baeriswyl) (TCM)
Our recent research was focussed on strongly correlated systems, including superconductivity from repulsive interactions and metal-insulator transitions induced by electron-electron interactions.