Superconductivity Understandings May Lead To Breakthroughs

 Superconductivity  

Researchers have found that an infrared laser pulse briefly modifies the structure of a high-temperature superconductor and removes its electrical resistance even at room temperature.

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n the 1980s, physicists first discovered a new class of materials based on ceramics. These materials conduct electricity at temperatures of around minus 200 degrees Celsius without losses, and were therefore called high-temperature superconductors. The compound yttrium barium copper oxide (YBCO) is one of these high-temperature superconductors and is one of the most promising materials for technical applications of the material, such as superconducting cables, motors and generators.

YBCOs crystal have a special structure: thin double layers of copper oxide alternate with thicker intermediate layers which contain barium as well as copper and oxygen. The superconductivity has its origins in the thin double layers of copper dioxide. This is where electrons can join up to form so-called Cooper pairs.

Cooper pairs can “tunnel” between the different layers, meaning they can pass through these layers like ghosts can pass through walls,in a type of quantum effect. The crystal only becomes superconducting however below a "critical temperature."

Above the critical temperature, this coupling between the double layers is missing, and the material becomes a poorly conducting metal.

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Andrea Cavalleri at the Max Planck Institute first discovered that when YBCO is irradiated with infrared laser pulses it briefly becomes superconducting at room temperature in 2013. The laser light had apparently modified the coupling between the double layers in the crystal.

The precise mechanism was unclear until the physicists were able to solve the mystery with an experiment at the Linac Coherent Light Source (LCLS) laser in the US, the world’s most powerful X-ray laser.

"It could assist materials scientists to develop new superconductors with higher critical temperatures and ultimately to reach the dream of a superconductor that operates at room temperature and needs no cooling at all."

“We started by again sending an infrared pulse into the crystal, and this excited certain atoms to oscillate,” explains Max Planck physicist Roman Mankowsky, lead author of the current study published in Nature. “A short time later, we followed it with a short X-ray pulse in order to measure the precise crystal structure of the excited crystal.”

According to the researchers, the infrared pulse had not only excited the atoms to oscillate, but had also shifted their position in the crystal as well. This briefly made the copper dioxide double layers thicker - by two picometres, or one hundredth of an atomic diameter - and the layer between them became thinner by the same amount. This in turn increased the quantum coupling between the double layers to such an extent that the crystal became superconducting at room temperature for a few picoseconds.

On the one hand, the new result helps to refine the still incomplete theory of high-temperature superconductors. “On the other, it could assist materials scientists to develop new superconductors with higher critical temperatures,” says Mankowsky. “And ultimately to reach the dream of a superconductor that operates at room temperature and needs no cooling at all.”

Until now, superconducting magnets, motors and cables required cooling to temperatures far below zero with liquid nitrogen or helium. If this complex cooling were no longer necessary, it would mean a breakthrough for this technology. This research may point to promising directions for understanding and development of higher temperature superconductors.


SOURCE  Max Planck Institute

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