Superconducting Materials, physics of electrons, crystals, metals, ceramics
World expert on superconductivity
"Follow your intuition. In my own experience, this has always paid off."
In French, taille means “cut” and fer is “iron,” so Louis Taillefer’s name literally means “cut iron.” One evening at Cambridge University in England, working in the famous Cavendish physics laboratory, Taillefer was making an alloy with special magnetic properties for his doctoral research. He had to melt a combination of platinum and iron in a high-tech furnace and then, with great patience, carefully draw it into a shiny, crystalline sample. Before beginning the melt, he needed to cut the precise amount of metal from a small rod. So there he was, sitting in the basement lab at night, slowly cutting this little piece of metal, and he suddenly broke out laughing: “Wow! This must surely be my vocation. I’m cutting iron, at last!”
Another time in the Cavendish lab, Taillefer was all alone. It was the week before Christmas 1985 and everyone else had left for the holidays. The room smelled of hot vacuum-pump oil. Taillefer first checked to make sure he was wearing no rings on his fingers. Then he removed any metal objects from his pockets, otherwise they might be heated by accident. The one-tonne induction furnace he was about to use could heat metal by sending out intense radio waves, so rings could get hot enough to burn. He cranked up the power to 100 kilowatts and the room buzzed with a steady 500-kilohertz hum. He moved a little water-cooled 10-centimetre copper crucible containing elemental uranium and platinum into position in the centre of the furnace coils under very high vacuum. Taillefer watched as the materials sputtered and melted together. The radio frequency emitted by the coils induced the electrons in the uranium and platinum to move so fast that they created enough heat to melt the metals into an alloy, called uranium platinide (UPt3). Now it was time to “zone it.” Taillefer slowly pulled the crucible out of the molten zone in such a way that the metal would solidify into a small ingot made of several perfect crystals. He was especially good at making ultra-pure compounds.
Purity is essential for this type of research because superconductivity and magnetism depend on it. Materials become superconductors when electrons spontaneously decide to pair together. Once paired, the electrons can move through the material effortlessly, transporting electricity perfectly with no resistance. Impurities can sometimes break up these pairs, causing problems in experiments. Superconductivity is a particular phase of a material, as, for example, when water is turning to ice. Many materials turn to superconductors at extremely low temperatures.
Taillefer was particularly excited because a brand new piece of equipment had just arrived, a special kind of refrigerator that could cool things down to near absolute zero, minus 273 degrees Centigrade, which is the coldest temperature in the universe. The new dilution refrigerator could freeze things to about 10 millikelvin, ten-thousandths of a degree above the point beyond which no further temperature drop is possible, absolute zero. Professor Mike Pepper had just bought the fridge and nobody had used it, so Taillefer wanted to run its first experiment, but for various reasons he had to wait a couple of months until spring break and it turned out that his was the second experiment with the fridge, but the first one that worked.
Before running his experiment, he had to go upstairs to a second-floor lab to prepare the sample. It was a low-temperature materials-characterization lab filled with electronics and cryogenic equipment for working with materials near absolute zero. Big vacuum-insulated Dewar flasks of super-cooled liquid helium and liquid nitrogen sat next to various microscopes, detectors and other instruments. Taillefer was excited as he placed the tiny rod of uranium platinide under a microscope. But he turned away for a moment and it rolled off the edge, shattering into about 25 little pieces all over the floor. Oddly, this turned out to be a lucky accident.
Taillefer wore surgical gloves to collect the shards and selected one for his experiment. He and his research team had access to the new fridge only 10 percent of the time, so he was anxious to try it as soon as possible. “At the time I was maniaque, as we say in French Canadian,” says Taillefer. He set up a special tiny coil of copper wire he had wound by hand under a microscope — 5,000 turns of 11-micron wire. The sample of uranium platinide was placed in the middle of the coil inside the refrigeration chamber. A powerful superconducting electromagnet swept a varying magnetic field over the sample as it was cooled to near absolute zero. Taillefer watched the pen of a chart recorder displaying voltage changes from the small copper pick-up coil around the sample. If the pen squiggled in a certain way (with sinusoidal oscillations) it would directly show quantization of electron energy coming from the circular motion of electrons in the metal sample. “It’s like the electrons are talking to us,” says Taillefer. “Boy, did we watch that pen.”
The experiment worked the first time, a rare occurrence in experimental science. Taillefer was attempting to measure the mass of electrons in a new class of materials called heavy electron metals, a potential superconductor of a new kind, in which extraordinarily strong electron interactions caused an electron mass increase, but nobody knew by how much. Seeing the quantized oscillation would provide a direct measure of that mass. The Cambridge group was competing with other teams in Europe and United States who also were trying to see these effects. Everyone was (and still is) trying to understand what is going on inside heavy electron metals like uranium platinide, so there was a race to get the results.
As it turned out, the piece of metal that Taillefer chose from the shattered rod had a particular crystalline orientation — the atoms making up the atomic crystalline structure of the metal — that lined up perfectly within the magnetic field. When Taillefer saw the first good series of oscillations coming out of the plotter, he ran to the classroom where his supervisor, Gil Lonzarich, was speaking, burst into the lecture hall and yelled, “We’ve got oscillations!”
At least three lucky events were involved: the uranium platinide that Taillefer made was of uncommon purity; the new fridge was available; and Taillefer, by chance, had placed the crystal in the apparatus with ideal orientation. It would be 10 years before another lab would duplicate Taillefer’s results from that lucky spring of 1986. A few months later, Taillefer graduated with a doctorate (PhD) from Cambridge University.
When Louis Taillefer was 16, he was a top student at his high school in Montreal but he was bored in class. Around that time he became friends with a farmer named Claude Côté. Taillefer’s father had a hobby farm near Valcourt, Quebec, and Côté’s farm was next door. Taillefer would see Côté working in the fields and would talk to him over the fence. “I became fascinated with farming,” says Taillefer. He asked his parents if he could quit school to become a farmer and work for Claude. His mom said, “Do what your heart tells you to do. If it means stopping school to be a farmer, then do it.”
When Taillefer showed up on Côté’s farm, Côté asked him to plow a field. Taillefer had limited experience driving a tractor. He was a city boy from Montreal. “I’d never even seen a cow up close,” he says. But Côté showed him the basics — start in the middle of the field, don’t cut too deep, don’t drive too fast — and said, “Go.” Taillefer spent days and days plowing fields. He was in heaven.
To Taillefer, Côté at 26 was a real-life example of a guy with no limits. Côté did everything himself. He was his own veterinarian, animal breeder and mechanic. He trained his own horses. Later he would go on to design and build a horse carriage and a house from scratch, cutting the trees and milling all the lumber. “He really taught me to have confidence in myself,” says Taillefer.
Sitting on that tractor proudly plowing fields, Taillefer felt good. But one day the engine started making noises and he drove the tractor back to the barn. He felt awful. He thought he had wrecked it, but Côté didn’t get upset at all. He just hauled the tractor to his garage, pulled out the engine, went to a scrapyard, got another crankshaft and popped it in.
“For Claude, everything was possible,” says Taillefer. “He showed me that a person can do anything.”
After a year on the farm Taillefer began to miss school, so he returned to Montreal to finish high school. At that point, he had no idea what he wanted to do at university. He was thinking of majoring in theatre, as it was his main interest in high school. Though he is French-speaking, Taillefer decided to go to McGill, an English university in Montreal, because he had won an entrance award to study mining engineering there. His mom said, “Bien, au moins t’apprendras l’anglais.” (“Well, at least you will learn English.”)
Even when he finished at the top of his class and won (together with his identical twin brother, Eric) the Anne Molson Gold Medal for top student in math or physics at McGill, Taillefer was not sure a life in physics was right for him, but he went to graduate school because that’s what everyone did. He was registered for Harvard University in Cambridge, Massachusetts, but won a Commonwealth scholarship to go to Cambridge University in England, for one year. “I took the opportunity because I had never been to Europe,”says Taillefer. At Cambridge he started working on a project, but after eight months he could not see the relevance of the work and was on the verge of dropping out. Fortunately, his supervisor, Gil Lonzarich, gave him a fascinating new project: a search for a theory of magnetism, something Professor Lonzarich had been working on himself in his spare time. Taillefer rapidly became absorbed with this new work and eventually called Harvard to say he would not be attending.
Magnetism was fascinating to Taillefer. While magnets are all around us, much of the physics of magnetism remains to be explained. Based on his doctoral research, Taillefer wrote a paper in 1985 presenting a theory that accounted for the so-called critical temperature of magnets — the point at which magnetism disappears in a heated metal. It was Taillefer’s first publication and is still one of the most highly cited papers on the topic.