Electrons take a detour in superconductors
Researchers from the Foundation for Fundamental Research on Matter, the University of Amsterdam, and the Leibniz Institute for Solid State and Materials Research IFW Dresden (Germany) have identified the primary pathway that electrons take in tunneling experiments on high-temperature superconductors. In such an experiment electrons 'jump' from a thin needle to a (superconducting) surface to be investigated. Knowledge about the pathway that the electrons then follow is important for the interpretation of earlier research on the electronic structure of superconductors. In this way, it contributes to the microscopic understanding of superconductivity. The researchers will publish their results 19 September in Physical Review Letters.
Atomic resolution
In scanning tunneling microscopy experiments researchers take a conducting needle, ending in a single atom, and bring it very close to a surface to be investigated. Even though there is no mechanical contact between the needle and the surface, a quantum mechanical effect (tunneling) allows for a current to flow if a voltage is applied between the needle and the surface. By measuring the current as function of voltage the researchers obtain information on the electronic structure of the surface directly under the needle with atomic resolution.
Theory and experiments
Researcher from Dresden modeled the tunneling process between an iron-arsenide superconductor and a Platinum STM-tip. They calculated the total tunneling current as well as the pathways followed by the electrons through the surface layers. It turns out that the pathway leading to the largest contribution in the tunneling current derives from the topmost layer of Barium atoms. The investigators from Amsterdam confirmed these findings experimentally through STM experiments on BaFe2As2 crystals. These results contribute to the search for the intrinsic properties of these materials relevant to the mechanism of high-temperature superconductivity, as these properties can now be distinguished from other effects.
Contact
Van der Waals - Zeeman Instituut, Universiteit van Amsterdam
Dr. Erik van Heumen +31 (0)20 525 63 75 / Prof. dr. Mark S. Golden +31(0)20 525 63 63
Institute for Theoretical Solid State Physics IFW Dresden
Prof.dr. Jeroen van den Brink +49 (0)351 465 93 80 / Dr. Klaus Koepernik +49 (0)351 465 93 60
Reference
'Surface Adatom Conductance Filtering in Scanning Tunneling Spectroscopy of Co-doped BaFe2As2 Iron Pnictide Superconductors' K. Koepernik, S. Johnston, E. van Heumen, Y. Huang, J. Kaas, J. B. Goedkoop, M. S. Golden, and J. van den Brink, Phys. Rev. Lett. 109, 127001 (2012).