Wednesday, July 1, 2009, 11:00 am — Bldg. 480 conference room
It has been now over 20 years since the discovery of the first high temperature superconductor by Georg Bednorz and Alex Müller and yet, despite intensive effort, no universally accepted theory exists about the origin of superconductivity in cuprates. A controversial issue on weather the electron-phonon interaction (EPI) is crucial for high-temperature superconductivity or weak and inessential has been one of the most challenging problems of contemporary condensed matter physics. First-principles calculations based on density functional theory (DFT) often predict a rather weak EPI insufficient to explain high transition temperatures in the framework of the conventional (BCS) theory. Hence many researchers maintain that the repulsive electron-electron interaction in novel superconductors is pairing and provides high transition temperatures without phonons. We as some other researchers are of the opinion that the EPI may be considerably enhanced by correlation effects beyond DFT. Here I present our recent theoretical results, which in conjunction with a number of other theoretical and experimental observations provide a definite answer to this fundamental question. Theoretical studies using advanced numerical (QMC) techniques have shown that purely repulsive models do not account for high-temperature superconductivity [1]. Besides, there is direct experimental evidence that EPI is an important player, e.g. from isotope substitution experiments, high resolution angle resolved photoemission (ARPES), earlier optical, neutron-scattering and recent pump-probe [2,3] and tunnelling [4] spectroscopes. Some time ago I proposed that the true origin of high-temperature superconductivity could be found in a proper combination of strong electron-electron correlations with a significant finite-range EPI so that low energy quasi-particles are small mobile polarons and/or bipolarons in cuprate superconductors [5]. We have shown that the conventional finite-range EPI explains the un
Hosted by: Ivan Bozovic
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