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Physicists Just Found the First Evidence That Superconductivity Can Be Left- or Right-Handed

Where electricity flows without resistance... but only in one direction.

FIONA MACDONALD
28 FEB 2017
 

Scientists have found the first evidence that superconductivity, one of the most intriguing and lucrative phenomena in physics, can be left- or right-handed. Or, more accurately, that superconducting materials can display chirality.

Chirality is frequently seen in nature - chiral materials are those that have mirror image versions of themselves that aren't identical, just like a left and a right hand. But until now, chirality and superconductivity - the ability for a material to transmit electricity with zero resistance - had never been found in the same material.

 

Now, an international team of researchers has observed a superconducting current flowing in only one direction through a chiral nanotube - the first observation of a chiral material acting as a superconductor.

This is important, because superconductivity is one of the most sought-after phenomena in physics. Right now, we see it occur when we cool certain materials down to very-chill temperatures below around  5.8 K (-267°C or -440°F).

When that happens, superconductive materials begin to shuttle electrons through them without any resistance, making them incredibly powerful.

Superconductivity is already used to create the strong magnetic fields in MRI machines and maglev trains, but if scientists can learn to harness it at more stable temperatures, it could revolutionise the way we shuttle electricity around the globe - current grids lose up to 7 percent of their electricity due to resistance.

Understandably, superconductivity is something scientists want to learn more about.

Prior to this, superconductivity had only been demonstrated in 'achiral' materials, which are materials that can be flipped and reflected any which way and will still be identical. That meant the superconductive current had always been seen to flow without resistance in both directions.

 

But a lot of materials out there are chiral, and with important effects, so scientists have been probing whether any of these could also be superconductive.

"Chirality of materials are known to affect optical, magnetic and electric properties, causing a variety of nontrivial phenomena," the researchers, led by Yoshihiro Iwasa from the University of Tokyo, Japan, write in Nature Communications.

One of the obvious choices for a chiral superconductor was carbon nanotubes, because they're chiral, superconducting, and commonly available, as Lisa Zyga notes for Phys.org.

But in previous experiments, researchers had only successfully demonstrated superconductivity happening in groups of nanotubes, not in individual nanotubes - which is something that needs to happen in order to determine chirality.

Now, Iwasa and his team has managed to do just that.

"The most important significance of our work is that superconductivity is realised in an individual nanotube for the first time," one of the researchers, Toshiya Ideue, told Zyga.

"It enables us to search for exotic superconducting properties originating from the characteristic (tubular or chiral) structure."

To do this, they used a two-dimensional superconducting material called tungsten disulfide.

They cooled a single tungsten disulfide nanotube down to 5.8 K (-267°C or -440°F) and ran a current through it, and observed it becoming superconducting - which means its normal resistance dropped by half.

The team then applied a magnetic field parallel to the nanotube, and observed small antisymmetric signals only travelling in one direction.

Chirality webQin et al., Nature Communications

"The asymmetric electric transport is realised only when a magnetic field is applied parallel to the tube axis," Ideue told Phys.org.

"If there is no magnetic field, current should flow symmetrically. We note that electric current should be asymmetric (if the magnetic field is applied parallel to the tube axis) even in the normal state (non-superconducting region), but we could not see any discernible signals in the normal state yet, interestingly, it shows a large enhancement in the superconducting region."

The team still isn't sure exactly what causes these asymmetric signals, but their next goal is to investigate them further, as they begin to explore the relationship between superconductivity and chirality.

If we can figure that out, it could help unlock the potential of superconducting 'diodes' that only allow electricity to flow in one direction, and could make up more sophisticated circuits in future.

It's early days, but we're now entering a new phase of superconductivity. Next step: getting it to occur stably at room temperature.

The research has been published in Nature Communications.

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