Condensed Matter Physics

This group´s research activities include topics both in experimental and theoretical condensed matter physics. As macroscopic properties of materials are determined by the structure down to micrometre and atomic scale, one fundamental aim of the group is to understand and establish and understand these relationships, making it possible to tailor materials properties for future applications and devices. Accordingly, a large fraction of the research is focused on studies of structure and properties of nanoscale systems and the connection to macroscopic physical properties. The members of the division work with a variety of experimental techniques, ranging from scanning tunneling microscopy, transmission electron microscopy, X-ray scattering, diffraction and imaging employing home laboratory and synchrotron radiation, for studying physical properties of materials and material structures. Two sub-areas of research are of particular interest for the research school, the X-ray scattering group and the Surface Science sub-groups.

The X-ray scattering group is working on the structural characterization of functional materials using X-ray scattering and imaging as their main tools. The emphasis is on self-assembled materials, typically in the form of ultrathin films, nanowires or nanoparticles. One special field of expertise is measuring and quantifying parameters such crystallinity, preferred orientation and molecular structure of materials for organic electronics, notably conjugated polymers and liquid crystals. The group has also recently expanded into coherent 3D imaging (tomography) of nanoscale objects.

Considerable efforts are also being devoted to developing mathematical models to account for the experimental data gathered at synchrotrons or in NTNU´s modern university laboratory. Increasingly, the focus is on “in situ” experiments, ranging from the surveillance of molecular self-assembly processes to measuring the structural response of functional materials, and even entire MEMS components, under the influence of external stimuli.

The group has a laboratory consisting of two setups for X-ray scattering and -diffraction, and one for X-ray imaging, and works cooperatively with researchers at the European Synchrotron Research Facility (ESRF) in France, the Hamburger Synchrotronstrahlungslabor (Hasylab) in Germany, and the Swiss Federal Institute of Technology (SLS – ETH) in Switzerland.

The surface science group has two major lines of research activities, one in surface chemistry/surface science and the other in nanoscale magnetism. The nanomagnetism research is dedicated to understanding the physics of magnetic structures at the nanoscale, particularly through the use of STM-based transport measurements to understand how charge and spin currents in materials interplay with the magnetization of materials. One main line of research is performed in conjunction with the Department of Electronics and Telecommunications (Prof. T. Tybell) to study functional metal oxides. Themes that we work on are:

  • Nanostructuring and magnetic properties of La1-xSrxMnO3 and oxide based heterostructures.
  • Current induced switching and coupling to macroscopic properties in GMR elements (metal and oxide based).
  • Spin pumping and high frequency dynamics < 40 GHz of ferromagnets.
  • Dynamics of anti-ferromagnets at short time scales.
  • Magnetotransport properties of quantized systems.
  • Studies of topologically protected surface states.
  • Scattering within and interfacing graphene/graphite.
  • Development and use of point contact spectroscopy for probing of physical properties (phonon modes, weak localization).
  • Studies of spin pumping and magnetodynamic base properties through both local and averaging techniques.
  • Instrument development.

The research is based primarily on synthesis and investigation of model systems, produced either through in situ growth or through nanoscale lithography processing.  Home-lab activities and extensive use of synchrotron radiation based experiments (electron photoemission, in the form of XPS as well as angle and spin-resolved ultraviolet  photoemission) form the experimental basis of these efforts. The home-lab operates three ultra high vacuum STMs, one with sources and electron energy analyser for UPS/XPS analysis and one specifically designed for magnetic field dependent point contact measurements and operation close to 4 K. In addition to this the group is building capacity for magnetodynamic measurements, in the form of ferromagnetic resonance set-ups and a 40GHz STM for cryogenic operation.

 

(Erik Wahlstrøm, Dag Breiby)