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High temperature superconductors

Superconductivity is one of those rare phenomena where quantum physics can be obser-ved at a macroscopic scale. It was discovered in conventionnal metals such mercury, soon after the first liquefaction of Helium, by H. K. Onnes in 1911. It took almost 50 years of in-tense research in order to formulate the BCS theory (named after J. Bardeen, L. Cooper and J. Schrieffer, who elaborated it) which describes superconductivity as a condensation of electron pairs, known as Cooper pairs. The formation of such a pair relies on the elec-tron-phonon interaction which is found to be attractive below a certain energy scale. BCS superconductors are thus known to be phonon mediated, meaning that exchange of pho-nons between two electrons provide the glue for the pair formation. In 1986, Bednorz and Müller discovered a new kind of superconductors called cuprates. At the time of this disco-very, the highest temperature below which superconductivity could be observed (critical temperature Tc) was found in Nb3Ge, with Tc 20 K. Cuprate superconductors rapidily showed critical temperatures of the order of 100 K, much higher than in conventionnal BCS superconductors. The highest Tc known today is found in a cuprate material and is as high as 164 K (half way from room temperature). Such high critical temperatures, combi-ned with other factors such as the fact that the parent cuprate coumpound is a Mott insula-tor, cast doubt about the BCS theory to be appropriated for a description of high-Tc super-conductivity. This was a new challenge for condensed matter physics : there has to be a new mechanism at play in those materials. High-Tc cuprate superconductors have been since then a field of tremendous research effort, in order to establish the mechanism of the electron pair formation in those systems. Please find below more information about how experiments in high magnetic fields can help solve this problem.

Member of the group :

Permanent members : Cyril Proust, Baptiste Vignolle, David Vignolles

Postdoc : David Le Boeuf

PhD students : Sven Baddoux, Stéphane Lepault

Former members : Cyril Jaudet (PhD), Julien Levallois (PhD)

Please find more information about :

Superconductors: the role they play today and why is it so cool to study them

High-Tc cuprates : phase diagram

Why do we need high magnetic fields to study high-Tc superconductors?

The Fermi surface of hole-doped cuprates : results from high magnetic field experiments in Toulouse