Laser pulses keep superconductors working at higher temperatures

Intense laser flashes remove the electrical resistance of a crystal layer of the alkali fulleride K3C60, a football-like molecule containing 60 carbon atoms(Credit: J.M. Harms/MPI for the Structure and Dynamics of Matter)

An international team of scientists led by the Max Planck Institute in Hamburg, Germany, has found a new mechanism allowing superconducting materials to maintain their properties at much higher temperatures than was previously possible. The advance brings the dream of mainstream maglev trains and highly energy-efficient electronics a little closer to reality.

When electrons flow through a conductor, their negative charge forces them to repel one another and bounce against the surrounding atoms. Electrons lose a good portion of their energy in this way, dissipating it as heat in an unwanted effect that heats up our laptops and decreases our smartphones' battery life.

But when cooled to a few degrees above absolute zero, the electrons in common materials like aluminium, tin, mercury and lead pair up to conduct electricity with no dissipation whatsoever. Ever since discovering this peculiar effect, called superconductivity, scientists have been trying to create man-made materials that can behave as a superconductor at higher and higher temperatures to pave the way for their mainstream use.

In a promising development, researchers Dr. Stephen Clark and colleagues may now have found a way to make existing superconductors work at higher temperatures, with possible applications spanning from MRI scanning to maglev trains and even fusion reactors.

For their experiment, the scientists took carbon and potassium buckyballs, which they knew behaved as superconductors at temperatures below 20 K (-253° C, -424° F) and shone a laser with mid-infrared optical pulses at them. As a result, they found that the material was still superconducting at a significantly higher temperature of 100 K (-173° C, -280° F).

The frequency of light chosen for the laser caused the buckyballs to vibrate. However, when the molecules were made to vibrate while also being kept at the lower temperature of 20 K, the material no longer behaved as a superconductor. According to Clark, this suggests that the researchers found a completely new state for superconductors that is better suited to higher temperatures, rather than simply enhancing the existing and already known superconducting state.

While a family of ceramic, copper-based materials known as cuprates are perhaps the most promising candidates for a room-temperature superconductor, their physics is not yet fully understood. Performing the study on the much simpler buckyballs will help scientists better grasp on this phenomenon before they can apply it to more promising materials.

"Whilst this is a small piece of a very large puzzle, our findings provide a new pathway for engineering and controlling superconductivity that might help stimulate future breakthroughs," says Clark.

The next step for the researchers will be to try and find superconductors that can be made to work at even higher temperatures, perhaps even at room temperature.

The study appears in the latest edition of the journal Nature.

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