Breakthrough in Superconductivity – Université de Sherbrooke Physicists Put an End to 20 Years of Debate

English: levitation of a magnet on top of a superconductor of cuprate type YBa2Cu3O7 cooled at -196°C. Français : lévitation d’un aimant au dessus d’un supraconducteur de type cuprate YBa2Cu3O7 refroidi à -196°C. (Photo credit: Wikipedia)

“If this state could persist at ambient temperature, it would profoundly transform our technological world”

Three physicists at the Université de Sherbrooke led an international team to first direct measurement of the critical magnetic field in cuprates, the most promising materials for superconductivity. This breakthrough resolves an enigma that has baffled researchers for 20 years and clears the way for major advances. The study is published in the prestigious journal Nature Communications.

A Dream Destination: Superconductivity at Ambient Temperature

When some materials are cooled to very low temperature, barely above absolute zero (-273 °C), they become superconductors, and their electrical and magnetic properties change radically. They acquire a nearly magical property: they carry electricity perfectly, without any energy loss.

The most promising superconducting materials are copper oxides, also called cuprates. They are, at present, the materials that become superconductors at the highest temperature, specifically -150 °C, which is halfway between absolute zero and ambient temperature.

So, for now, these materials must still be cooled down to extremely low temperatures before they become superconducting. “If this state could persist at ambient temperature, it would profoundly transform our technological world,” maintains Louis Taillefer, holder of the Canada Research Chair in Quantum Materials and the study’s senior investigator. The transmission of electricity around the world would be radically changed, for example. “This great dream will become possible when scientists understand how to increase the maximum value of the critical temperature by a factor of two or more.”

The team has just identified one of the main mechanisms limiting the critical temperature of cuprates, which opens a new direction in determining how to increase it.

A Million Times Stronger than the Earth’s Magnetic Field

In addition to their critical temperature, another fundamental property of superconductors is their critical magnetic field. What is its value in cuprates?

In order to measure the critical field of cuprates, the team investigated their capacity to conduct heat. A material’s heat conductivity turns out to be very sensitive to the onset of superconductivity. The very first direct measurement of this critical field in cuprates was made possible as the result of a novel approach developed by the group of researchers working on the physics of quantum materials at the Université de Sherbrooke.

“The key to our discovery,” says Nicolas Doiron-Leyraud, “was developing equipment at Sherbrooke that can make such measurements under very strong magnetic fields.” The team then traveled to specialized laboratories in Tallahassee, Florida, and Grenoble, France, where magnetic fields up to 1 million times the earth’s field are produced.

“Once there, we realized that it was the first time that anyone had made such an attempt, explains Gaël Grissonnanche, PhD student in physics and first author on the paper. The first measurements on the first day… and it worked!”

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