The nature of the superconduc ting state in the cuprates

21.03.2016 16:00 – 18:00

Ever since the discovery of the phenomenon superconductivity, the flow of electrical current without any resistive losses, scientists have been intrigued by the question what causes it. One of the unquestionable principles of superconductivity is, that electrons pair up to form Cooper pairs. Since pairs of electrons are effectively bosons, they can -and do- condense in a superfluid state. The big question is however why these pairs would form in the first place since, after all, electrons in vacuum rather move away from each other due to the Coulomb repulsion. Some workers in the field (in particular but not exclusively PW Anderson and AJ Leggett) have approached this question from a general perspective, by formulating statements about the behaviour of the Coulomb energy and of the kinetic energy as a function of temperature of the electron liquid when a material shifts from normal metal to superconducting.
Experimentally these quantities can be measured using various different kinds of spectroscopic probes, including high precision low temperature optical spectroscopy. On general grounds one than expects the interaction energy to become reduced when the electrons form pairs, while at the same the kinetic energy increases. Our experimental optical data, presented in this colloquium, demonstrate aforementioned changes of energy when tuning the material from normal to superconducting, and elucidate the nature of the superconducting state in the cuprates.

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Bâtiment: Ecole de Physique

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