Keywords: user research (29) spintronics (90) quantum materials (26)

News    09.02.2018

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

Zita Hüsges


           



You might also be interested in
  • <p>(a) Neutronen-Eigenspannungsmessung an einer Schwei&szlig;probe aus handels&uuml;blichen Stahl, (b) Magnetfeldmessung, (c) Schwei&szlig;nahtquerschliff.</p>SCIENCE HIGHLIGHT      21.12.2018

    Neutronenforschung hilft bei der Entwicklung von zerstörungsfreien Prüfverfahren

    Materialermüdung zeigt sich häufig zuerst daran, dass im Innern des Materials Bereiche mit stark unterschiedlichen Eigenspannungen aneinandergrenzen. An der Neutronenquelle BER II am HZB hat ein Team der Bundesanstalt für Materialforschung und –prüfung (BAM) die Eigenspannungen von Schweißnähten aus ferromagnetischem Stahl analysiert. Die Ergebnisse helfen zerstörungsfreie elektromagnetische Prüfverfahren zu verbessern. [...]


  • <p>The data show that In the case of the two-layer graphene, a flat part of bandstructure only 200 milli-electron volts below the Fermi energy.</p>SCIENCE HIGHLIGHT      10.11.2018

    Graphene on the way to superconductivity

    Scientists at HZB have found evidence that double layers of graphene have a property that may let them conduct current completely without resistance. They probed the bandstructure at BESSY II with extremely high resolution ARPES and could identify a flat area at a surprising location. [...]


  • <p>Shown are the magnetic fluxlines inside a superconducting sample of lead in two different directions. The scale bar is 5 mm. </p>SCIENCE HIGHLIGHT      02.10.2018

    Neutrons scan magnetic fields inside samples

    With a newly developed neutron tomography technique, an HZB team has been able to map for the first time magnetic field lines inside materials at the BER II research reactor. Tensorial neutron tomography promises new insights into superconductors, battery electrodes, and other energy-related materials. [...]




Newsletter