IQ scientists unravel yet another mystery of high-temperature superconductors

As they propagate through an electrical conductor, electrons undergo collisions that dissipate their energy and give rise to an electrical resistance. A team led by Louis Taillefer and Patrick Fournier, Professors at Sherbrooke and members of the Institut Quantique, now shows that electrons in cuprate high-temperature superconductors dissipate as much energy as quantum mechanics allows, a major breakthrough reported in Nature Physics.

A time will come when superconductors will revolutionize our daily life, in areas as diverse as energy transmission, medicine, and communications. As of today, a family of copper-oxide materials – the cuprates – provides perhaps the most promising candidates for raising the temperature at which superconductivity occurs, from low temperatures typically below -150^o C to ambient temperature. However, these are complex materials and the mechanism at the origin of the lossless resistance still escapes our understanding. This is one of the main conundrums of physics.

In their so-called normal state, outside of the superconducting phase, cuprates display an enigmatic electrical resistance: it varies linearly as a function of temperature, whereas metals are known to display a quadratic variation. First identified 30 years ago, this property is a central mystery of cuprates, comparable in significance to their spectacular superconductivity. The IQ team now discovered the root cause of this phenomenon: at low temperatures, no matter which cuprate material is looked at, the electrons hit an upper limit in the amount of energy they can dissipate as they travel through a specimen and undergo collisions. This universal limit is known as the Planckian limit, which is governed by the fundamental laws of quantum mechanics.

“Comparing our data on different cuprate materials, it became increasingly clear that a universal underlying mechanism was involved. This Planckian limit finally provides a solid foundation for drafting a theory of the linear resistivity of cuprates” comments Anaëlle Legros, first author of the Nature Physics paper and leader of the project in the context of her doctoral studies. “We now have a wide open field of exploration, since this characteristic was also observed in several other families of quantum materials. We seem to have touched upon a fundamental mechanism of nature, whose implications are unsuspected” adds her PhD advisor, Louis Taillefer. And indeed, this phenomenon appears to have multiple ramifications that are becoming apparent through recent papers on black holes, gravity, and quantum information.

Realized in collaboration with Cyril Proust at Toulouse and Dorothée Colson at Saclay, this study brought together, with Taillefer and Fournier, 4 scientists of the Laboratoire International Associé France-IQ – the Laboratoire Circuits et Matériaux Quantiques. This Sherbrooke-France partnership was recently highlighted in November 2018 by the Adrien-Pouliot prize of the Acfas. It is also a brilliant example of co-tutoring, since Taillefer and Colson jointly supervised Anaëlle Legros, who is now pursuing her scientific career as a postdoctoral fellow at Johns Hopkins University in the US. The Canadian Institute for Advanced Research was also at the core of this work, since Proust, Fournier, and Taillefer are all members of its Quantum Materials Program. The Gordon & Betty Moore Foundation contributed to funding this study, via a grant to Taillefer as part of its program on Emergent Phenomena in Quantum Systems.