User research at BER II: New insights into high-temperature superconductors
Sketch of the stripe order: The charge stripes, which are superconducting, are shown in blue. Reprinted with modifications from Physical Review Letters.
The colour plots show measured data of the magnetic order (left) and the magnetic excitations (right). The slight mismatch, only visible in high resolution data, demonstrates that the excitations do not originate from the magnetically ordered state. Reprinted with modifications from Physical Review Letters.
After 30 years of research, there are still many unsolved puzzles about high-temperature superconductors - among them is the magnetic “stripe order” found in some cuprate superconductors. A Danish research team has taken a closer look at these stripes, using high-resolution neutron scattering at the spectrometers FLEXX (HZB) and ThALES (ILL, Grenoble). Their results, now published in Physical Review Letters, challenge the common understanding of stripe order, and may contribute to unveil the true nature of high-temperature superconductivity.
It has been known for about 30 years that cuprate superconductors become superconducting at surprisingly high temperatures – often above the boiling point of liquid nitrogen (-196 °C). This makes them particularly interesting for applications. Research has revealed that the mechanism which leads to the formation of the superconducting state is different for the cuprates than for conventional superconductors. However, despite intensive studies, this unusual mechanism is still not properly understood. Scientists hope that by understanding what makes high-temperature superconductors special, they will eventually be able to find a material that is superconducting at room temperature.
In the cuprates, superconductivity is intimately connected with the magnetic properties – in stark contrast to conventional superconductors, where magnetism destroys superconductivity. For several cuprate compounds, an unusual state is found where stripes of magnetic order alternate with stripes of charge, which are superconducting (see figure). Also magnetic excitations, apparently associated with the magnetic stripes, have been observed.
A team from Niels Bohr Institute, University of Copenhagen, Denmark, has performed neutron scattering experiments to take a closer look at the magnetic stripes. Using the spectrometers FLEXX (HZB) and ThALES (ILL, Grenoble), they were able to analyse the stripes with very high resolution. They deduced from their data that the magnetic stripe order and the magnetic excitations, although also stripe-like, are not related to each other, but actually originate from different regions in the sample. The comparison with other studies suggests that phase separation into a magnetic and a superconducting phase occurs, and that the striped magnetic excitations belong to the superconducting phase. This model requires a careful re-consideration of many other studies on cuprate superconductors which assume that the stripe order and excitations have the same origin. The results were now published in Physical Review Letters.
Published in Phys. Rev. Letters (2018): "Distinct Nature of Static and Dynamic Magnetic Stripes in Cuprate Superconductors", H. Jacobsen, S. L. Holm, M.-E. Lăcătuşu, A. T. Rømer, M. Bertelsen, M. Boehm, R. Toft-Petersen, J.-C. Grivel, S. B. Emery, L. Udby, B. O. Wells, and K. Lefmann.
DOI: 10.1103/PhysRevLett.120.037003
- Battery research with the HZB X-ray microscopeNew cathode materials are being developed to further increase the capacity of lithium batteries. Multilayer lithium-rich transition metal oxides (LRTMOs) offer particularly high energy density. However, their capacity decreases with each charging cycle due to structural and chemical changes. Using X-ray methods at BESSY II, teams from several Chinese research institutions have now investigated these changes for the first time with highest precision: at the unique X-ray microscope, they were able to observe morphological and structural developments on the nanometre scale and also clarify chemical changes.
- BESSY II: New procedure for better thermoplasticsBio-based thermoplastics are produced from renewable organic materials and can be recycled after use. Their resilience can be improved by blending bio-based thermoplastics with other thermoplastics. However, the interface between the materials in these blends sometimes requires enhancement to achieve optimal properties. A team from the Eindhoven University of Technology in the Netherlands has now investigated at BESSY II how a new process enables thermoplastic blends with a high interfacial strength to be made from two base materials: Images taken at the new nano station of the IRIS beamline showed that nanocrystalline layers form during the process, which increase material performance.
- Alternating currents for alternative computing with magnetsA new study conducted at the University of Vienna, the Max Planck Institute for Intelligent Systems in Stuttgart, and the Helmholtz Centers in Berlin and Dresden takes an important step in the challenge to miniaturize computing devices and to make them more energy-efficient. The work published in the renowned scientific journal Science Advances opens up new possibilities for creating reprogrammable magnonic circuits by exciting spin waves by alternating currents and redirecting these waves on demand. The experiments were carried out at the Maxymus beamline at BESSY II.