17-Nov-2014 - Linköping University

Self-doping may be the key to superconductivity in room temperature

Swedish materials researchers at Linköping and Uppsala University and Chalmers University of Technology, in collaboration with researchers at the Swiss Synchrotron Light Source (SLS) in Switzerland investigated the superconductor YBa2Cu3O7-x (abbreviated YBCO) using advanced X-ray spectroscopy.

YBCO is a well-known ceramic copper-based material that can conduct electricity without loss (superconductivity) when it is cooled below its critical temperature Tc=-183° C. Since the resistance and energy losses are zero in superconductors, there exist many technologically interesting and energy-saving electrical applications as well as benefits to the transport industry. Electromagnets in electric motors can be made smaller with stronger magnetic fields that are more powerful yet consume less energy; magnetic levitating trains that exploit superconductor technology can reach higher speeds by avoiding friction against rails.

On the other hand, the necessity of cooling these materials to low temperatures remains to be an obstacle one would like to eliminate. Therefore, one of the major objectives of superconductor research is trying to find a material that is superconducting at room temperature. However, the mechanism that underlies high-temperature superconductivity is still not entirely understood. In this work, the researchers have made a discovery that may shed new light on this phenomenon. X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) was used for measuring YBCO at room temperature and at -258° C, which is far below Tc.

What makes YBCO special as a superconductor is that it is made up of two types of structural units, i.e. stacked "planes" of copper oxide, assumed to carry the superconducting current, but also separate "chains" of copper oxide in between. The role of the chains in YBCO has puzzled scientists ever since the discovery of its superconducting properties in 1987. One had realized early on that Tc can be influenced in the material synthesis procedure by varying the "oxygen doping", and thus the length of the chains.

It has long been assumed that the doping level of the material was solely determined by the structure of the chains at the time of synthesis. By contrast, the new experimental results show that the chains in YBCO react to cooling by supplying the copper oxide planes with positive charge (electron-hole), a mechanism called self-doping. By combining RIXS and model calculations, the researchers also found that self-doping is accompanied by changes in the copper-oxygen bonds that link the planes with the chains.

This groundbreaking discovery of self doping in YBCO challenges the traditional understanding of the mechanism of superconductivity in copper-based high-temperature superconductors, which assumes a constant doping level in the copper oxide planes. Some previous temperature-dependent experiments will now have to be re-evaluated in this new light, and thereby help us come closer to finally solving the riddle of high temperature superconductivity. Next, the researchers plan to conduct a more detailed temperature dependent study to determine if restructuring and redistribution of the orbital occupation occurs exactly at the phase transition to superconductivity or if it already occurs at a higher temperature in the so-called pseudogap region.

  • M. Magnuson, T. Schmitt, V.N. Strocov, J. Schlappa, A.S. Kalabukhov and L.-C. Duda; "Self-doping processes between planes and chains in the metal-to-superconductor transition of YBa2Cu3O6.9."; Scientific Reports 4, 717 (2014).
Facts, background information, dossiers
  • Uppsala University
  • Linköping University
  • Chalmers University…
More about Linköping University
  • News

    New porous material promising for making renewable energy from water

    One prospective source of renewable energy is hydrogen gas produced from water with the aid of sunlight. Researchers at Linköping University, Sweden, have developed a material, nanoporous cubic silicon carbide, that exhibits promising properties to capture solar energy and split water for h ... more

    LiU researchers first to develop an organic battery

    Researchers at the Laboratory of Organic Electronics, Linköping University, have for the first time demonstrated an organic battery. It is of a type known as a "redox flow battery", with a large capacity that can be used to store energy from wind turbines and solar cells, and as a power ban ... more

    From nanocellulose to gold

    When nanocellulose is combined with various types of metal nanoparticles, materials are formed with many new and exciting properties. They may be antibacterial, change colour under pressure, or convert light to heat. "To put it simply, we make gold from nanocellulose", says Daniel Aili, ass ... more

More about Uppsala University
  • News

    How chemicals in plastic may cause lower IQ levels

    The chemical bisphenol F (found in plastics) can induce changes in a gene that is vital for neurological development. This discovery was made by researchers at the universities of Uppsala and Karlstad, Sweden. The mechanism could explain why exposure to this chemical during the fetal stage ... more

    Producing more sustainable hydrogen with composite polymer dots

    Hydrogen for energy use can be extracted in an environmentally friendly way from water and sunlight, using photocatalytic composite polymer nanoparticles developed by researchers at Uppsala University. In laboratory tests, these "polymer dots" showed promising performance and stability alik ... more

    Ancient enzymes can contribute to greener chemistry

    A research team at Uppsala University has resurrected several billion-year-old enzymes and reprogrammed them to catalyse completely different chemical reactions than their modern versions can manage. The method can be used to develop sustainable solutions within biotechnology, such as for e ... more

More about Chalmers University of Technology
  • News

    New electronic paper displays brilliant colours

    Imagine sitting out in the sun, reading a digital screen as thin as paper, but seeing the same image quality as if you were indoors. Thanks to research from Chalmers University of Technology, Sweden, it could soon be a reality. A new type of reflective screen - sometimes described as 'elect ... more

    World first concept for rechargeable cement-based batteries

    Thanks to unique research from Chalmers University of Technology, Sweden, such a vision could someday be a reality. Researchers from the Department of Architecture and Civil Engineering recently published an article outlining a new concept for rechargeable batteries - made of cement. The ev ... more

    Big breakthrough for 'massless' energy storage

    Researchers from Chalmers University of Technology have produced a structural battery that performs ten times better than all previous versions. It contains carbon fibre that serves simultaneously as an electrode, conductor, and load-bearing material. Their latest research breakthrough pave ... more