Superconductivity was initially discovered by Heike Kamerlingh Onnes in 1911 in pure Mercury where he noticed resistivity abruptly dropped below a certain temperature. This temperature, so-called the superconducting critical temperature Tc, saw its limit increased year by year with new alloys of pure metals up to 20K until the 50’s. At this time, thanks to the successful BCS theory explaining the pairing mechanism of electrons by a phonon exchange, the topic of superconductors seemed to be fully understood. With the discovery of unconventional superconductors in the 80’s, the thematic has found a great interest, especially with the high-Tc cuprates where Tc can reach 100K at ambient pressure. However, the pairing mechanism of these superconductors is not due to a phonon exchange and remains an enigma for Physicists. The phase diagram of these unconventional superconductors encloses a superconducting dome located around the critical doping of an ordered phase. For cuprate superconductors, the phase diagram shows a complexity leading the origin of the pairing mechanism puzzled. During this talk, I will present recent data on cuprate materials demonstrating the presence of quantum criticality in the phase diagram which could be a candidate for the pairing mechanism. We will try to extend to other unconventional superconductors like the SrTiO3 diluted metal showing superconductivity around a presupposed quantum critical point of a ferroelectric order.
Dr. Bastien Michon obtained his PhD degree in October 2017. His PhD was realized in an international collaboration between the groups of Pr. Louis Taillefer in Sherbrooke (Canada) and Pr. Thierry Klein in Grenoble (France). During this PhD, Dr. Bastien Michon developed strong skills in experimental Physics such as transport and specific heat under high magnetic field (up to 35T) and very low temperature (down to 400mK). From February 2018, he is currently doing a Postdoctoral position in the group of Pr. Dirk van der Marel in Geneva (Switzerland) where he developed an expertise on infrared spectroscopy and optics. His principal research achievements are based on cuprate superconductors and other unconventional superconductors, but he is also interested on other quantum materials such as Weyl semi-metals.
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University of Geneva
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