Louis Taillefer Superconducting Materials, physics of electrons, crystals, metals, ceramics

World expert on superconductivity

"Follow your intuition. In my own experience, this has always paid off."

The Story

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.

As a young scientist...

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.

The Science

Louis Taillefer is a materials scientist, a physicist who specializes in the behaviour of electrons in matter. He considers himself a modern-day alchemist — medieval chemists who worked at turning ordinary metals into gold or silver — because his research involves cooking up materials that have never been made before. He uses super-powerful furnaces in which metals and ceramics are melted by electric arcs (the same as a lightning bolt), intense radio waves or focused beams of super-hot light. Elements of unequalled purity are combined in new and precise ways. The ultimate goal: a superconductor, a material in which electrons can move happily with no resistance at all.

Many materials can be superconductors, but only at extremely low temperatures. Scientists have known for about 100 years that superconductivity can occur in aluminum, lead, mercury, tin and other metals, but it only happens below -250°C. This is near absolute zero, which is a temperature of -273°C (-460°F). Materials scientists use the Kelvin temperature scale, which uses the same units as Celsius but places “zero” at absolute zero, not as we register it in the Celsius or Fahrenheit scales. Nothing can be colder than absolute zero, which technically means the absolute lack of entropy, a physical property of matter sometimes called thermal agitation or disorder — the need for atoms to jiggle around. Think of it this way: when liquid water turns to ice, it loses entropy. The water molecules that were zooming around all over the place in the liquid are now locked into a solid crystal and they can’t move as much. They are also colder. By lowering the temperature, the water went through a phase change, from liquid phase to solid phase. It’s the same material, but a different physical phase of matter, hard and solid instead of a soft, flowing liquid.

The same thing happens with superconductivity. It’s just another phase change. When some metals are cooled down to near absolute zero, around one to 10K, they become superconductors. This temperature at which they change phase to superconductors is called the critical point. So, for instance, aluminum becomes superconducting at 1.2K and mercury at 4.1K. Pretty cold.

In 1986, superconductivity got hotter. Two Swiss physicists working at IBM Labs in Zurich, Karl Alexander Müller and J. Georg Bednorz, discovered that a certain type of copper oxide became a superconductor at temperatures around 40K — quite a lot warmer than ever before. Within a year, scientists around the world began creating similar materials and raised the temperature of superconductivity to 93K. It took the world of science by storm. Müller and Bednorz won the 1987 Nobel Prize for their discovery. Today the “warmest” superconductor works at about 133K.

Liquid nitrogen has a temperature of 77K and is cheaper than milk, so we can now easily create an environment where superconductivity works. Before this, superconductors had to be cooled with liquid helium, which costs about the same as whisky (30 times more than liquid nitrogen) and does not last very long.

The new so-called high-temperature superconductors (HTS) have led to new applications such as ultra-high-performance radio frequency filters for use in cellphone network base stations or high-current electricity transmission. In the summer of 2001 three 400-foot HTS cables were installed in Detroit, Michigan, capable of delivering 100 megawatts of power. Superconductors are also appearing in high-speed “maglev” (magnetic levitation) trains in Japan, Germany and Singapore. These trains have no wheels and ride on a frictionless magnetic “cushion.” Future HTS applications include ultra-fast computers capable of operating at petaflop speeds, much cheaper and smaller scanners for medical imaging, ultra-efficient electrical generators and new electric motors twice as efficient as and half the size of conventional motors.

The mathematical explanation of superconductivity was worked out in 1957 and is called BCS theory, after the three American scientists who discovered it: John Bardeen, Leon Cooper and Robert Schrieffer. In a normal conductor, flowing electrons collide with crystal impurities that slow them down and cause electrical resistance. In a superconductor this does not happen because the electrons pair up and form a coherent quantum state, making it impossible to deflect the motion of one pair without involving all the others. So collisions have no impact and there is no resistance. While BCS theory works for conventional superconductors, it does not explain the behaviour of the new high-temperature superconductors. Taillefer thinks the mechanism is a purely electronic interaction, possibly involving the magnetic spin of the electrons.

His work demonstrates a classic strength of the scientific technique: Scientists invent theories that predict and explain the behaviour of the physical world. However, they keep testing and retesting these theories, especially under extreme conditions, to see where they break down. In this way they discover newer and better theories that reveal the essential qualities of nature. Taillefer’s most recent experiments question a basic theory explaining why good electrical conductors are also good heat conductors. He showed that under certain conditions (extreme cold and pressure), a type of copper-oxide superconductor appears to conduct electricity and heat differently. Experiments like Taillefer’s inspire new, improved theories to explain more of the physical world.

How superconductivity works. Click to enlarge.

1. Superconductivity is a phase of matter. This graph shows where phase changes occur in high-temperature copper-oxide superconductors, depending on the temperature (in Kelvin) and the number of electrons in its crystal structure. (Holes are the places left when atoms in the surrounding crystal matrix pull electrons away. Holes are like electrons, because they can move around and carry charge in conductors or superconductors.) Superconductivity occurs in the half-circle region at the bottom, when the material has from 5 to 25 percent holes and the temperature is below about 130K. At low-electron hole concentrations, the material becomes an insulator, while at high concentration it is a conventional metal — a good electrical and heat conductor. Remarkably, by changing electron concentration only 5 percent, the material goes from a perfect insulator (incapable of transporting any electricity) to the strongest known superconductor (a perfect conductor of electricity).

2. Physicists who work at low temperatures use the Kelvin (K) scale to measure temperature. Use the three thermometers to compare where common temperatures appear on more familiar Celsius and Fahrenheit scales.

3. The superconducting material YBa2Cu3O7, yttrium-barium-copper oxide, is part of the mineral family called “Perovskites.” This brittle ceramic material was one of the first high-temperature superconductors discovered, in 1987. Superconductivity occurs in the copper-oxide planes (speckled grey balls) as a result of electron interactions that are not entirely understood, but could involve the formation of Cooper pairs. Yttrium (dark blue), Barium (light blue).

4. Electrons have spin, which makes them into tiny little magnets. They also carry a negative charge. As charges repel, so do electrons normally strongly repel each other. However, in special circumstances they may be drawn to each other to form so-called Cooper pairs. This occurs when the surrounding crystal matrix, made of positively charged atoms, is locally deformed by the passage of a single electron, which in turn attracts a second electron in its wake. Think of the way two people can roll toward each other on a waterbed; it works something like that. In general, a Cooper pair of electrons “join” in such a way that their total spin is cancelled out (that is, the spin of one points up and the other points down, cancelling each other.) Because of this, a Cooper pair behaves like a single particle with zero spin and mass twice that of a single electron. But Cooper pairs do not behave independently of each other like single electrons in a normal metal conductor. They form a single coherent quantum state, which means that instead of having random behaviour, they all act in exactly the same way. In this sense, superconductivity is a large macroscopic quantum phenomenon.

5. Once a current gets going in a superconductor, it can be made to flow forever in a circular loop. This is the closest we come to perpetual motion in nature. Superconducting coils can become powerful lightweight electromagnets. Mounted on a Shanghai maglev train, with conventional magnets or electromagnets in the guideway, the train floats on magnetic fields, moving with no friction except air resistance. Such maglev trains cruise at 580 kilometres per hour. The train shown does not use high-temperature superconductors. It works with conventional superconductors requiring liquid helium, which is very expensive.

6. Electrons have two major features, charge and spin. Charge is responsible for the phenomenon of electricity — when electron charge flows, an electric current is created. Spin is responsible for magnetism — when all the electron spins in a material line up in the same direction, the material becomes a magnet. Scientists like Taillefer find new properties of materials as they discover how electron spin and charge behave in different materials. One new theory suggests that in high-temperature superconductors, electrons may lose their usual integrity, so that spin and charge are no longer carried together. If such spin/charge separation indeed occurs, then the fundamental particles in materials are no longer electrons but can be thought of as of two smaller particles, “chargeons” and “spinons.” In his research, Louis Taillefer is observing unusual phenomena that may be caused by such spin/charge separation.

So You Want to Be a Physicist

It was pure chance that Louis Taillefer became a physicist. He simply accepted a scholarship to study mining engineering at McGill University. “If some other place had given me an award in biology, I would have gone there,” he says. At McGill he soon switched to geophysics, but he enjoyed the fundamental science so much that he ultimately graduated with an honours degree in pure physics. Taillefer likes to tell young people, “Go in some direction, but don’t feel you need to be stuck there. Go with your intuition and change, readjust to what interests you. Feel free to switch to subjects where you feel more at home.”

As a graduate student, Taillefer’s quest for more relevant research brought out Gil Lonzarich’s passion for theoretical work on magnetism. This in turn inspired the young Taillefer to discover something essential in the natural world. Now that Taillefer himself supervises graduate students, he finds it to be the most satisfying part of his job as a university professor for the same reason. Seeing students find their own path is a wonderful feeling for him, and the only way this happens is if he gives them the freedom to do so. “The key point is that people must go where they feel their inspiration,” says Taillefer. “I give my students the freedom to develop as independent scientists but also to follow their destiny as individuals.”

 

Typical physics careers include specialties in electronics, communications, aerospace, remote sensing, biophysics, nuclear, optical, plasma or solid state physics, astrophysics and cosmology. Some physicists concentrate on experiments, while others prefer theory alone.

Mystery

Is room-temperature superconductivity possible? So far, scientists have created materials that are superconductors at 133K, which is still -140°C — mighty cold. Taillefer wonders if we will ever find a material that is a superconductor at room temperature (293K). Other big questions in materials science: What makes some materials magnetic, and others not? And why does heat destroy the magnetic properties of some materials more rapidly than others?

Explore Further

Jean Matricon, Georges Waysand (translator) and Charles Glashausser, The Cold Wars: A History of Superconductivity, Rutgers University Press, 2003.

Michael Tinkham, Introduction to Superconductivity, second edition, Dover Books, 2004.

Explanation of maglev trains.

Scientific American magazine featured 12 Events That Will Change Everything in their June 2010 issue. Click on icon no.6 (out of 12), in the top right corner (after the introduction animation). Then click on "Interview with Dr. Louis Taillefer" and "The Canadian Institute for Advanced Research" to see some video clips of Louis Taillefer talking about his science.

Career Advice

So You Want to Be a Physicist

 

It was pure chance that Louis Taillefer became a physicist. He simply accepted a scholarship to study mining engineering at McGill University. “If some other place had given me an award in biology, I would have gone there,” he says. At McGill he soon switched to geophysics, but he enjoyed the fundamental science so much that he ultimately graduated with an honours degree in pure physics. Taillefer likes to tell young people, “Go in some direction, but don’t feel you need to be stuck there. Go with your intuition and change, readjust to what interests you. Feel free to switch to subjects where you feel more at home.”

As a graduate student, Taillefer’s quest for more relevant research brought out Gil Lonzarich’s passion for theoretical work on magnetism. This in turn inspired the young Taillefer to discover something essential in the natural world. Now that Taillefer himself supervises graduate students, he finds it to be the most satisfying part of his job as a university professor for the same reason. Seeing students find their own path is a wonderful feeling for him, and the only way this happens is if he gives them the freedom to do so. “The key point is that people must go where they feel their inspiration,” says Taillefer. “I give my students the freedom to develop as independent scientists but also to follow their destiny as individuals.”

 

Typical physics careers include specialties in electronics, communications, aerospace, remote sensing, biophysics, nuclear, optical, plasma or solid state physics, astrophysics and cosmology. Some physicists concentrate on experiments, while others prefer theory alone.

Career ideas:

  • research scientist, physics
  • research scientist, electronics
  • research scientist, communications
  • research scientist, aerospace
  • research scientist, remote sensing
  • nuclear physicist
  • optics physicist
  • plasma physicist
  • solid state physicist
  • astrophysicist
  • cosmologist
  • experimental physicist

The Person

Birthdate
October 28, 1959
Birthplace
Montreal, Québec
Residence
Sherbrooke, Québec
Family Members
  • Father: Laurent Taillefer
  • Mother: Andrée Lepage
  • Spouse: Louise Brisson, Architect
  • Four brothers, including an identical twin
  • Two children: Raphaël, Charlotte
Personality
Open minded, happy, optimistic
Favorite Music
Bach, Leonard Cohen, Richard Desjardins
Other Interests
Waldorf school, cross country skiing, kids
Title
Professor
Office
Département de physique, Université de Sherbrooke
Status
Working
Degrees
  • BSc. (Physics), McGill, Montreal, 1982
  • PhD. (Physics), Cambridge, England, 1986
Awards
  • Herzberg Medal (Canadian Association of Physicists), 1998
  • E.W.R. Steacie Fellowship (NSERC), 1998
  • Scientist of the year, Radio Canada, 2002
  • Fellow of the American Physical Society, 2003
  • Brockhouse Medal (Canadian Association of Physicists), 2003
  • Prix Marie-Victorin, Government of Quebec, 2003
  • Fellow, Royal Society of Canada, 2007
  • Medal of Achievement (Canadian Association of Physicists), 2008
  • Member of the Order of Canada, 2010
  • Killam Prize in the Natural Sciences, 2012
Mentor
Gil Lonzarich, Cambridge professor who taught high standards and to have confidence that you can push the limits. Claude Côté, farmer who showed that you could do anything, make anything, there are no limits if you trust your abilities.
Last Updated
May 10, 2012
Popularity
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