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Leconte Prize

par Jean-Claude GARREAU, Le directeur du laboratoire, Thérèse HUET, Webmestre - publié le

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The disorder is also common in nature than chaos, two phenomena having a very real impact on human activities. Thus, at the global level, the chaotic behavior of the atmosphere makes the unpredictable weather and the climate in the long term. In the microscopic world, the disorder affects strongly transport phenomena in materials. In particular, the disorder is partly responsible for the electrical resistance of materials, with consequences for the fundamental understanding of the physics of these systems, but also with practical and societal consequences, given the importance of electrical conduction in technology current.

At the fundamental level, the model for understanding the influence of disorder on conductivity is the famous Anderson model that defies physicists since 1958. It predicts a surprising phenomenon named "Anderson localization" : the possibility of total suppression of conductivity even very low levels of disorder, and to very low temperatures. This phenomenon can only be explained by quantum mechanics. More generally, the model predicts the existence of a phase transition between a situation where the system is an insulator and a situation where it is conductive : the metal-insulator transition of Anderson.

However, it is very difficult to study quantum phenomena in such good conditions in "real" materials, where multiple external influences disturb the system and complicate the interpretation. Fortunately, it is possible to study under near ideal conditions using laser cooled atoms, a technique that provides atoms at temperatures a million times colder than intergalactic vacuum, we speak of ultracold atoms, which are, in fact, the coldest gases in the universe. We can then measures the quantum properties of these systems with previously unattainable precision.

Best of all, it possible to produce ultra-cold atoms systems where very clean "quantum" chaos acts of disorder. But this chaos can be controlled extremely precisely. One example is the "atomic rotator hit." It is using this system as Jean-Claude Garreau and his team were able to study the metal-insulator transition of Anderson with a precision and an unprecedented level of detail. They were able to give a complete characterization of this transition, and in particular measure, for the first time worldwide, a quantity that uniquely characterizes a phase transition : its "critical exponent". The study of this physics thanks to ultra-cold atoms opens the way to a better understanding of the true conductivity of solid materials, with potential impact on the improvement of their properties.

Voir en ligne : Les lauréats des prix thématiques attribués en 2015