19 Mar 2015

Superconductivity breakthroughs

SASKATOON – The Canadian research community on high-temperature superconductivity continues to lead this exciting scientific field with groundbreaking results coming hot on the heels of big theoretical questions.

The latest breakthrough, which will be published March 20 in Science, answers a key question on the microscopic electronic structure of cuprate superconductors, the most celebrated material family in our quest for true room-temperature superconductivity.

This result is the product of a longstanding close collaboration between the University of British Columbia Quantum Matter Institute and the Canadian Light Source. In fact, this is the third Science paper to come out of this remarkably fruitful collaboration this past year, and the first to feature an all-Canadian effort.

The collaborators work at the forefront of research into high-temperature superconductors, an exciting class of materials exhibiting superconductivity at temperatures as comparatively warm as -100?C. As frigid as such temperature may sound, it outperforms by far traditional superconductors, which operate at closer to -270?C, or a few degrees from absolute zero – the point where all motion stops.”

In the superconducting state, electricity flows with absolutely no resistance, which means no energy is lost and no heat is generated. Combined, these properties allow for large ‘supercurrents’ that could not be realized in ordinary wires.

For this reason, superconductors are already used to provide the large magnetic fields needed for Magnetic Resonance Imaging, but the cooling systems needed to make them work are costly and impede other potential uses. Some of the major, transformative applications of room-temperature superconductivity include magnetic levitation trains and lossless power lines. (Imagine getting rid of that pesky delivery charge on your energy bill—room temperature superconductivity could make it possible.)

The paper’s lead author, Riccardo Comin, a UBC graduate from Andrea Damascelli’s group and now a post-doctoral fellow at the University of Toronto, compares the movement of electrons in a superconductor to birds flying in formation, coherently and without collisions. In physics-speak, the electrons move coherently and in phase, and no energy is lost as they drift smoothly along.

In cuprate superconductors, another state blocks and interacts with superconductivity: the charge-density-wave, in which the electrons assume a static pattern, different from the pattern that the material’s crystal structure defines.

You can also think of the superconducting electrons like cars on a highway, all moving the same speed and direction, the picture of efficiency. But the charge-density-wave state acts like a patterned traffic jam: no movement, anywhere.

Understanding what causes this pattern is thought to be a key step to understanding superconductivity, but even pinning down the nature of the pattern has been elusive. Major theoretical models predict either a parallel line structure, or a checkerboard pattern. Unfortunately, even with advanced synchrotron techniques, it has proved impossible to see the difference between the two models.

That is, until Comin’s latest results in Science, which show that the cuprate superconductor in question has a stripe-like pattern rather than a checkerboard one. The UBC-CLS team used an unconventional experimental approach to reconstruct a 2-dimensional model of the static electron pattern from 1-dimensional scans—much like the tomographic reconstructions used for medical purposes.

These results offer new fundamental insights helping hone the search for room temperature superconductivity. However, more challenging questions remain. Among these puzzles: What is the driving force behind the tendency of electrons to move together coherently in the superconducting state, and how can the superconductivity transition temperature be further enhanced? Despite almost 30 years of history, the field of high temperature superconductivity is more alive than ever.

More information, including a copy of the paper, can be found online at the Science press package at http://www.eurekalert.org/jrnls/sci. You will need your user ID and password to access this information.

Figure: Sketch of the static patterns for (a) 1D stripy charge order and for (b) 2D checkerboard charge order, within the 2D Cu-O plane.
Cite: Comin, Riccardo, 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 
This work is the result of a longstanding collaboration between researchers from the University of British Columbia Quantum Matter Institute—primarily the research groups of George Sawatzky, Doug Bonn, and Andrea Damascelli—and Canadian Light Source’s scientists Feizhou He (right) and Ronny Sutarto (left). Damascelli and Riccardo Comin (centre) led the work included in this paper.

Story: Victoria Martinez

About the CLS:

The Canadian Light Source is Canada’s national centre for synchrotron research and a global centre of excellence in synchrotron science and its applications. Located on the University of Saskatchewan campus in Saskatoon, the CLS has hosted over 2,000 researchers from academic institutions, government, and industry from 10 provinces and 2 territories; delivered over 32,000 experimental shifts; received over 8,300 user visits; and provided a scientific service critical in over 1,000 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.

Synchrotrons work by accelerating electrons in a tube to nearly the speed of light using powerful magnets and radio frequency waves. By manipulating the electrons, scientists can select different forms of very bright light using a spectrum of X-ray, infrared, and ultraviolet light to conduct experiments.

Synchrotrons are used to probe the structure of matter and analyse a host of physical, chemical, geological and biological processes. Information obtained by scientists can be used to help design new drugs, examine the structure of surfaces in order to develop more effective motor oils, build more powerful computer chips, develop new materials for safer medical implants, and help clean up mining wastes, to name a few applications.

For more information visit the CLS website or contact:

Mark Ferguson 
Communications Coordinator 
1 (306) 657-3739 
mark.ferguson@lightsource.ca

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