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.
Three-dimensional charge density wave in cuprate films.
Over the past several years, charge density waves have turned out to be the major competitor of high-temperature superconductivity in copper oxides. In resonant x-ray scattering experiments on YBCO thin films grown epitaxially on SrTiO3, we made the surprising discovery that three-dimensional charge order is present in the absence of magnetic fields, and persists to much higher temperatures than the two-dimensional order investigated in prior work. The results offer new insight into the unusual stability of charge density waves in YBCO, as well as fresh perspectives for experiments elucidating the influence of charge order on the electronic properties of cuprates without the need to apply high magnetic fields.
M. Bluschke et al., Nature Comm. 9, 2978 (2018)
Measurement and control of exchange interactions in nickelates.
Two new papers report important progress towards the goal of designing new magnetic states in oxide heterostructures. First, we used high-resolution inelastic x-ray scattering to directly determine the magnon dispersion relations and exchange interactions in an epitaxial film of NdNiO3 . We then established an elementary model system – NdNiO3 slabs embedded in a non-magnetic NdGaO3 matrix – to show that both collinear and non-collinear magnetic structures can be realized, depending on the slab thickness.  The crossover between both spin structures can be qualitatively understood in a low-energy spin model with the competing exchange interactions determined by RIXS. Magnetic slabs thus provide new perspectives for research on complex magnetism, in analogy to two-dimensional materials created by exfoliation.
 Y. Lu et al., Phys. Rev. X 8, 031014 (2018)
 M. Hepting et al., Nature Physics (2018), doi: 10.1038/s41567-018-0218-5