Can’t get your new material to lose all electrical resistance? Try mulling it in red wine
WONDERING what to do with any booze left over from your Christmas party? Most people would be happy to pour the dregs down the sink and keep the untouched stuff for later. But Yoshihiko Takano has another idea: donate it to the search for superconductivity.
Takano, a physicist at Japan’s National Institute for Materials Science in Tsukuba, discovered a few months ago that alcoholic drinks can transform fairly ordinary materials into amazing ones. Unlikely as it sounds, booze could help to unlock one of the biggest mysteries in physics: superconductivity.
Advertisement
Superconductors are revered because they conduct electricity with zero resistance. That makes them fascinating from a theoretical viewpoint, and also points to brilliant applications. If you could make overhead power lines from superconducting cables they would lose barely any of the electrical energy they carry, saving money and cutting carbon dioxide emissions. Superconductors also repel magnetic fields, which means they can levitate anything containing materials with the merest hint of magnetism – including trains.
With such remarkable properties, you might expect to find superconductors in use everywhere. The reason you don’t is that they need to be extremely cold to work properly. Most only superconduct at temperatures close to absolute zero. This has been a source of frustration ever since superconductors were discovered, in 1911, when Dutch physicist Heike Kamerlingh Onnes found that he could make mercury lose all electrical resistance by chilling it to 4.2 kelvin (-269 °C) in liquid helium. Many more metallic superconductors have since been discovered, but none works above about 25 K, which is far too cold for anything but the most specialised applications.
A big breakthrough came in 1987 when Alex Müller and Georg Bednorz at the IBM Zurich Research Laboratory in Switzerland that became a superconductor at the positively balmy temperature of 92 K. Their work triggered a frenzy of research into so-called “high-temperature” superconductors. “Everyone went mad,” says Ted Forgan at the University of Birmingham in the UK. “There were lots of reports of ‘unidentified superconducting objects’ as people tried to push to higher temperatures.”
Unlike the original superconductors, these new materials are ceramics containing layers of copper and oxygen atoms. Crucially, they work at temperatures that can be reached using liquid nitrogen, which makes them much more practical. “Liquid nitrogen costs half the price of milk, and there is an infinite amount of it”, Forgan explains.
Today the world record for the warmest superconductor is held by a blend of mercury, barium and calcium plus the standard copper and oxygen layers. It superconducts at 135 K. Similar materials are being tested in power cables and for levitating trains.
However, 135 K is still well below room temperature. To make further progress, researchers would love to know what makes high-temperature superconductors so special.
Unfortunately, nobody has much of a clue. Although we understand metallic superconductors, there is no equivalent theory for high-temperature ones. “We’ve spent a quarter of a century and still don’t understand them,” says Forgan. It probably has something to do with the layers of copper and oxygen, which are common to all the high-temperature superconductors.
That’s where Takano’s boozy discovery might help. In 2008, another group of researchers at the Tokyo Institute of Technology stumbled upon an entirely new type of superconductor. Made from iron, arsenic, oxygen and lanthanum, it sent the superconducting world wild (New Scientist, 16 August 2008, p 31).
Tests soon showed that these iron-based superconductors had much in common with high-temperature ones, especially in structure, with layers of iron and arsenic that are similar to those of copper and oxygen. Though they don’t work at especially high temperatures, the hope is that they will lead to new theoretical insights into high-temperature superconductivity.
The craze for iron soon reached Takano’s group, which began playing around with a simplest recipe based on iron and tellurium. In one experiment they tried replacing some of the tellurium with sulphur. The resulting material was hopeless, utterly failing to superconduct. And that might have been the end of the story if one of Takano’s students hadn’t been dumped by his girlfriend.
As he licked his wounds, the student began neglecting his duties. So when Takano asked him for fresh samples of iron tellurium sulphur to test, he had none to offer. Instead he brought along an old sample that had been left lying around in the open air for weeks. To everyone’s amazement, it showed signs of life ().
Why would a useless compound suddenly start superconducting? Suspecting that exposure to the air had something to do with it, Takano and his colleagues made a fresh batch, then exposed samples to pure nitrogen or pure oxygen. Others they kept in a vacuum, or submersed in water.
Only the samples soaked in water turned into superconductors. “We found that the coexistence of water and oxygen is important,” says Takano.
That set him wondering what else might have the same effect. Inspiration soon arrived in the form of Yoichi Kamihara, one of the discoverers of iron-based superconductors. He visited the institute in March 2010 to give a lecture. So Takano did what anyone would do under the circumstances: he organised a booze-up.
Soaked in alcohol
During the party, Takano had a brainwave. He instructed one of his students to spirit away some of the drinks – not for drinking, but for experiments. “I thought of it because I like alcohol very much,” Takano says. They pilfered wine, beer, whisky, sake and shochu, a Japanese liquor.
Later, in the lab, they heated the alcoholic drinks to 70 °C to speed up whatever reactions might be taking place, and soaked their samples in them for 24 hours. Then they tested for superconductivity.
The were striking. All the drinks worked, with red wine streets ahead of the rest (see graph).
The results aren’t simply down to the amount of alcohol in the drinks. Whisky and shochu are much stronger than wine but did not work as well. Takano’s team also tried using increasingly alcoholic mixtures of water and ethanol, but none worked as well as the beverages.
“Whisky and shochu are stronger than wine but did not work as well at making materials superconduct”
Takano cannot yet explain why being mulled in red wine should turn iron tellurium sulphur into a superconductor. He suspects it is something to do with antioxidant molecules called polyphenols, which are abundant in red wine. Beyond that he is stumped.
His team is now gearing up to study the crystal structure of iron tellurium sulphur before and after it is immersed in red wine. They hope to discover the mechanism that induces superconductivity and perhaps find some clues that could help us finally get to grips with high-temperature superconductors.
Like a good claret, Takano’s work is taking time to mature. “People thought it sounded a bit of a joke at first,” says Forgan. “But I think it’s a real effect.” Takano himself has received lots of supportive messages on Twitter. “Please use good red wine” has been a popular reaction. It’s anyone’s guess what will happen to the leftovers…
