Physics of strongly correlated electron systems

Optical spectroscopy

Neutron Scattering

Raman Scattering

TRISP spectroscopy

Theory

The department uses neutron and X-ray diffraction and spectroscopy as well as optical spectroscopy and Raman scattering to explore the structure and dynamics of materials with strong electron correlations. We also have a strong effort in the development of new spectroscopic methods. As the close collaboration between experimentalists and theorists is essential for the progress in this field, a small theory group operates within the department.

News

Chemical substitution is widely used to modify the charge carrier concentration (``doping'') in complex quantum materials, but the influence of the associated structural disorder on the electronic phase behavior remains poorly understood. We synthesized thin films of the prototypical high-temperature superconductor La2-xCaxCuO4 with minimal structural disorder and characterized their doping levels through measurements of the optical conductivity. We find that high-temperature superconductivity  is stable up to much higher doping levels than previously found for analogous compounds with higher levels of disorder.  The results imply that doping-induced disorder is the leading cause of the degradation of superconductivity for large carrier concentration, and they open up a previously inaccessible regime of the phase diagram of high-temperature superconductors to experimental investigation. more
The FeO2 square-lattice compound Sr3Fe2O7 exhibits a charge-ordering transition that had remained "hidden" to standard diffraction probes for more than fifty years. Neutron Larmor Diffraction and Resonant X-ray Scattering have now revealed a surprisingly simple “checkerboard” charge-ordering pattern in the FeO2 layers. As the checkerboards in adjacent layers are stacked in a nearly random fashion, the corresponding diffraction features are strongly broadened, thus explaining the "invisibility" to standard probes. The solution of the fifty-year-old Sr3Fe2O7 conundrum holds an important lesson for research on other hidden-order materials as well. more
Valentin Zimmermann has received a prize of the Faculty for Physics and Mathematics at the University of Stuttgart for his MSc degree in Physics. The prize was bestowed at the Faculty's annual Summer Event. more
The exactly soluble Kitaev model embodies key concepts in condensed matter physics such as topological spin-liquid states and emergent Majorana fermions, and RuCl3 has emerged as an important model system for Kitaev physics in solids. We have used resonant inelastic x-ray scattering with our new IRIXS spectrometer to determine the exchange interactions in RuCl3, which can now serve as the basis for theoretical work on this system. Since IRIXS only requires micrometer-sized crystals, our approach has the potential to evolve into a powerful screening tool for the rapidly expanding list of spin-liquid candidate materials.

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