03 Jun 2015

Physicists map electron structure of superconductivity's 'doppelgänger'

SASKATOON / VANCOUVER - Physicists have painted an in-depth portrait of charge ordering-an electron self-organization regime in high-temperature superconductors that may be intrinsically intertwined with superconductivity itself.

In two complementary studies-published in Nature Materials this week and Science in March-University of British Columbia researchers confirm that charge ordering forms a predominantly one dimensional 'd-wave pattern'.

“Everything we can learn about the structure of charge ordering gets us a step closer to understanding how it's intertwined with, and potentially competes with, superconductivity,” says Riccardo Comin, lead author on both papers who conducted the research while a PhD student at UBC. Comin is now a post-doctoral fellow at the University of Toronto.

Charge ordering creates instabilities in cuprate superconductors at temperatures warmer than -100 degrees Celsius. It causes some electrons to reorganize into new periodic static patterns that compete with superconductivity. The reason behind this competition has remained elusive until these studies demonstrated that charge ordering and superconductivity share the same underlying symmetry.

“Intriguingly, superconducting pairs of electrons also exhibit a so-called d-wave configuration,” says UBC physicist Andrea Damascelli, leader of the research team and senior fellow with the Canadian Institute for Advanced Research's Quantum Materials Program. “So this gives more credence to the possibility that both phenomena are siblings feeding off an underlying common interaction.”

In March's Science paper, Comin, Damascelli and colleagues investigated cold samples of yttrium barium copper oxide using x-rays and discovered that charge ordering produces a striped pattern, meaning the electrons self-organize along one direction rather than in two directions. However, when the temperature cools down far enough, charge ordering dies off and superconductivity takes over, allowing electrons to travel freely with no resistance, no longer constrained to one dimension.

The two studies were possible thanks to the longstanding collaboration between UBC and the REIXS beamline at the Canadian Light Source, where all the x-ray experiments were performed.

“Combined,” says Comin, “our recent investigations provide a complete resolution of the symmetry of the charge order in cuprates.”

Scientists using the REIXS beamline at the Canadian Light Source have discovered superconductivity's 'doppelgänger' in the form of charge ordering. From left: CLS Research Associate (REIXS) Ronny Sutarto, Riccardo Comin, PhD student at the University of British Columbia and now post-doctoral fellow at the University of Toronto, and CLS Beamline Scientist (REIXS) Feizhou He. Photo available in Flickr.
Cite: Comin, R., et al. "The symmetry of charge order in cuprates." arXiv preprint arXiv:1402.5415 (2014).doi:10.1038/nmat4295 ; Comin, R., et al. "Broken translational and rotational symmetry via charge stripe order in underdoped YBa2Cu3O6+ y." Science 347.6228 (2015): 1335-1339. DOI: 10.1126/science.1258399

About high-temperature superconductors:

Superconductivity--the phenomenon of electricity flowing with no resistance--occurs in some materials at very low temperatures. High-temperature cuprate superconductors are capable of conducting electricity without resistance at record temperatures, higher than the boiling point of liquid nitrogen. Because of their unrivalled characteristics, they represent the best candidates to advance current superconductor technology, which includes a broad range of applications such as: MRI, high-precision magnetometry, levitating high-speed trains, and lossless power lines.

About the Canadian Light Source Inc.:

The CLS is the brightest light in Canada-millions of times brighter than even the sun-used by scientists to get incredibly detailed information about the structural and chemical properties of materials at the molecular level, with work ranging from mine tailing remediation to cancer research and cutting-edge materials development.

The CLS has hosted over 2,500 researchers from academic institutions, government, and industry from 10 provinces and 2 territories; delivered over 40,000 experimental shifts; received over 10,000 user visits; and provided a scientific service critical in over 1,500 scientific publications, since beginning operations in 2005. The CLS has over 200 full-time employees.

CLS operations are funded by Canada Foundation for Innovation, Natural Sciences and Engineering Research Council, Western Economic Diversification Canada, National Research Council of Canada, Canadian Institutes of Health Research, the Government of Saskatchewan and the University of Saskatchewan.

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