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Strongly correlated electron systems

Many interesting systems in modern solid-state research can not be described by any effective single-particle wave function because inter-particle correlations dominate the microscopic behavior. Here, exotic phases of matter can emerge featuring exceptional topological properties, degree of entanglement, and quasi-particle excitations. Due to the related unexpected and unusual macroscopic properties, such quantum materials promise novel and rich functionality but are still a great challenge for our understanding. This understanding will benefit from illuminating related complex behaviors by a widespread set of experimental techniques and stimuli in a way that maximizes comparability of the results from different experiments. In the past years, HZB studies on superconductors and related transition metal oxides produced important results: The exploration of La1.8−xEu0.2SrxCuO4 revealed a first example of charge order developing undisturbed by any structural phase transition in a high-Tc compound with suppressed long-range superconductivity. The observation of this type of static charge order opened the door for many subsequent successful observations of similar phenomena in almost all known cuprate superconductors. Although charge order is only short-ranged in these materials, resonant elastic soft x-ray scattering provided the required sensitivity to observe this subtle ordering phenomenon. One of the present goals in this field is to achieve a final general understanding of the relation of charge order and high-Tc superconductivity. To this end, we not only explore the response of charge order and superconductivity to modifications produced via thin-film heteroepitaxy and external applied fields but proceed in continuously extending the set of available experimental tools and stimuli.
HZB studies on 5f-electron based magnetism focused on the determination of magnetic-field driven phase transitions in uranium compounds such as U(Ru0.92Rh0.08)2Si2 and U2Pd2In, mainly using neutron scattering in extremley high magnetic fields at the unique High-Field-Magnet at BER II.
In the following we present a few examples of research carried out in the field of strongly correlated electron systems within the last few years.

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


Above the phase transition at 25.8 Tesla U2Pd2In  exhibis a complex magnetic ordering pattern © HZB

Reciprocal space mapping of three YBCO films grown on STO (001)

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

enlarged view

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.