Unravelling the mystery of superconductivity

Doctors often use magnetic resonance imaging (MRI) to see inside a patient's body, but the underlying technology, known as nuclear magnetic resonance (NMR), can be used to see atoms inside a material. Unlike an MRI, which produces an image by aligning the magnetic spins of hydrogen atoms in the body's tissues and fluids, NMR helps researchers study the behaviour of magnetic and superconducting materials.

"I'm interested in materials that show a very strong quantum nature," said Takashi Imai, a professor of condensed matter physics at McMaster University. "If we want to see the quantum nature of electrons in materials, we need to go to a low temperature." By cooling a material to near absolute zero (-273°C), the electrons often undergo a unique quantum phase transition. In comparison to water, which undergoes a phase transition from a liquid to a solid when it freezes, the material may become magnetic or superconductive.

Superconductors are unique because they allow electrons to travel forever without any resistance or loss of energy through heat. Unlike conventional superconductors, which become superconductive when they undergo a phase transition near absolute zero, high-temperature superconductors, such as copper oxides and recently discovered iron arsenides, undergo this phase transition at much higher temperatures, sometimes above the boiling point of liquid nitrogen (-196°C). These high-temperature superconductors open up possibilities for practical applications using more cost-effective liquid nitrogen.  "It's still very cold, but nitrogen is very cheap because we breathe nitrogen in the air," said Imai.

The electrons in these unconventional superconductors possess a "spin," behaving like tiny magnets with north and south poles, and their fluctuations are believed to play a key role in the mysterious superconducting mechanism. Unique quantum phenomena can be observed in unconventional superconductors exposed to high pressure or strong magnetic fields, whereas applying a magnetic field to a conventional superconductor will destroy its superconductivity.  A major goal of Imai's research is to shed microscopic light on these quantum phenomena with NMR spectroscopy.

Imai's research wouldn't be possible without his lab, which he describes as "one of the best equipped labs in Canada." His students also benefit from the experience they gain by working in his lab. The skills they learn can be applied to PhD level research and beyond. Since students often don't know what they're capable of accomplishing, Imai encourages them to realize their full potential. "I tell them, ‘Why don't you try this?'" When they knock on his door to show him their latest discovery, it's a "rewarding moment" for him.