Strongly correlated electron systems

HZB studies of superconductors and related transition metal oxides have produced important results in the past few years. The study of charge order in La1.8xEu0.2SrxCuO4 revealed a first example of  static charge order independent of a structural phase transition and in the absence of long-range magnetic order. While charge order is not very well developed in this material, resonant soft x-ray diffraction provided the required sensitivity to observe the subtle ordering phenomenon. Similar is true for the recent observation of long-range incommensurate charge fluctuations in (Y,Nd)Ba2Cu3O6+x proving the concept that superconductivity competes with other orders in cuprate superconductors. The main goal in this field is to achieve a final general understanding of the interplay of charge ordering and high-Tc superconductivity with a present focus on manipulating charge order in thin film heterostructures and by external stimulus.

A different research topic is the complex charge ordering and associated magnetic ordering in CeRuSn. This compound has been extensively studied combining neutron and synchrotron x-ray diffraction with x-ray absorption spectroscopy.

In the following we present a few examples of research carried out within the last few years.

For a full list of publications of our institute klick here.

URuSi high field

Starting at a magnetic field strength of 23 Tesla, additional spots appear on the neutron detector that reveal the new magnetic order in the crystal. © HZB


Angular dependence within the a-b plane of the macroscopic saturation magnetization in bulk DyScO3. © APS


Phase diagram of the electron-doped cuprate superconductor compound Nd2-xCexCuO4 as a function of doping and temperature. The blue and red data points indicate the boundaries for the occurrence of charge order. © APS

Scanning electron microscopy in combination with EELS electron spectroscopy permits to visualise atomic positions of the individual atoms in the heterostructure: Superconducting regions of YBaCuO are identified by yttrium (blue) and copper (pink), the ferromagnetic layers by manganese (green) and lanthanum (red). Courtesy MPI Stuttgart.

Crystal structures of HgBa2CuO4+δ and YBa2Cu3O6+δ

Discrete Fourier transform of the conductance map; the corners of the image represent the atomic Bragg peaks at (+/-2π/a, 0) and (0, (+/-2π/b). The discrete Fourier transform is mirror-symmetrized and normalized to its average value. The central peak (d 0.2) corresponds to long
wavelength inhomogeneity of the conductance map. © AAAS

Modeled Fermi surface for hole-doping p = 0.12 for the interacting case, which is computed via the inclusion of the selfenergy SPG(k, w) and a further Gaussian smearing representing the effective experimental resolution. ©AAAS

The incident photon polarization can be parallel (p) or perpendicular (s) to the scattering plane. The real and reciprocal spaces are sketched in the front and rear plane, respectively. In the real-space image, the Cu 3dx2 − y2 and O 2p orbitals are shown. © AAAS

A schematic representation of the CeRuSn AF structure, projected onto the ac plane. 2a × 1b × 5c unit cells corresponding to the undistorted crystal structure of the CeCoAl type are shown. Magnetic moments are represented by arrows.© IOP