Physics of strongly correlated electron systems

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.

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Hun-ho Kim's doctoral dissertation "Uniaxial pressure study of charge density waves in a high-Tc cuprate superconductor" was selected for the Springer Thesis Award, which implies publication in book form in the Springer Theses series. Hun-ho Kim had graduated with distinction from the University of Stuttgart in 2020.In this thesis work, Hun-ho Kim performed an elegant series of resonant and non-resonant x-ray scattering experiments on the high-temperature superconductor YBa2Cu3O(6.67) under highly homogeneous uniaxial pressure and demonstrated the power of this method to modulate the interplay between superconducting and charge-density-wave (CDW) phases without introducing disorder and inhomogeneity. Specifically, he showed that uniaxial pressure enhances short-range-ordered CDWs in the copper-oxide planes and confirmed that the underlying order parameter is uniaxial, thus conclusively resolving a long-standing debate (H.H. Kim et al., Phys. Rev. Lett. 126, 037002 (2021)). He also discovered a three-dimensionally long-range ordered CDW that competes strongly against superconductivity, and showed that it is induced by softening of an optical phonon, in close analogy to classical structural phase transitions (H.H. Kim, M. Souliou et al., Science 362, 6418, 1040-1044 (2018))  His work on uniaxial pressure tuning opens up many new perspectives for research on high-temperature superconductors and other quantum materials. more

Our team at the Max Planck Institute for Solid State Research, in collaboration with the Max Planck Institute for Chemical Physics of Solids in Dresden, the Karlsruhe Institute of Technology, and the European Synchrotron Radiation Facility in Grenoble, France, applied a new approach to the investigation of charge density waves (CDW) in high-Tc superconducting cuprates. We combined uniaxial strain with resonant x-ray scattering (RXS) to explore a segment of the phase space of correlated electrons in the cuprates that had previously been inaccessible. Our findings clarify the nature of the CDW while demonstrating that the combination of uniaxial strain and RXS can become a powerful tool to shine light onto the complex interplay of electronic correlations in quantum materials.

 

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An international research team with scientists from the Max Planck Institute for Solid State Research in Stuttgart, together with collaborators from FELIX Laboratory and Radboud University in Nijmegen, the University of Bialystok, and Delft University of Technology, has demonstrated that shaking atoms in a crystal for a short time can lead to a permanent switching of magnetization. Ultrafast modification of the crystal field environment has the potential to become the most universal way to manipulate magnetization. It could be the starting point for innovative IT concepts such as ultrafast opto-spintronic devices.

 

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