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

November 13, 2014

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.

Their findings are published in the Nature journal Science Reports.

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.
-end-
Article: Self-doping processes between planes and chains in the metal-to-superconductor transition of YBa2Cu3O6.9; M. Magnuson, T. Schmitt, V.N. Strocov, J. Schlappa, A.S. Kalabukhov and L.-C. Duda; Scientific Reports 4, 717 (2014).

DOI: 10.1038 / srep07017, Published: November 12, 2014.

Linköping University

Related Superconductivity Articles from Brightsurf:

New kind of superconductivity discovered
Superconductivity is a phenomenon where an electric circuit loses its resistance and becomes extremely efficient under certain conditions.

Room temperature superconductivity creeping toward possibility
The possibility of achieving room temperature superconductivity took a tiny step forward with a recent discovery by a team of Penn State physicists and materials scientists.

A 'breath of nothing' provides a new perspective on superconductivity
Zero electrical resistance at room temperature? A material with this property, i.e. a room temperature superconductor, could revolutionize power distribution.

New Princeton study takes superconductivity to the edge
The existence of superconducting currents, or supercurrents, along the exterior of a superconductor, has been surprisingly hard to find.

Superconductivity: It's hydrogen's fault
Last summer, it was discovered that there are promising superconductors in a special class of materials, the so-called nickelates.

How a magnet could help boost understanding of superconductivity
Physicists have unraveled a mystery behind the strange behavior of electrons in a ferromagnet, a finding that could eventually help develop high temperature superconductivity.

New study explains why superconductivity takes place in graphene
Theoretical physicists take important step in development of high temperature superconductors.

Better studying superconductivity in single-layer graphene
A new study published in EPJ B demonstrates that an existing technique is better suited for probing superconductivity in pure, single-layer graphene than previously thought.

Stressing metallic material controls superconductivity
No strain, no gain -- that's the credo for Cornell researchers who have helped find a way to control superconductivity in a metallic material by stressing and deforming it.

First report of superconductivity in a nickel oxide material
Scientists at SLAC and Stanford have made the first nickel oxide material that shows clear signs of superconductivity - the ability to transmit electrical current with no loss.

Read More: Superconductivity News and Superconductivity Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.