Zhiping Yin, Rutgers University

Abstract: The century long history of superconductivity has shown us the ubiquity of this fabulous phenomenon and the Nobel Prize-winning Bardeen-Cooper-Schrieffer (BCS) theory provides us a successful framework of (conventional) superconductivity. Nevertheless, a complete understanding of unconventional superconductors is still lacking and a practical guide as where to find high temperature superconductors is missing, despite extensive experimental and theoretical research in the last few decades. Several proposals were advocated at different times but none of them was specific enough nor entirely correct. In the past few years, we have carried out comprehensive theoretical and computational studies of the new iron-based superconductors and the celebrated bismuthates and chloronitrides using state-of-the-art many-body electronic structure methods. For all of these superconductors, we find that electronic correlation plays a very important role, just as in the cuprate and heavy fermion superconductors. In the iron-based superconductors, we find strong antiferromagnetic spin fluctuations and identify a novel orbital-antiphase superconducting pairing symmetry while in the bismuthates we find strong electron-phonon coupling induced by electronic correlation. I will discuss how our studies put extra constraints on and/or modify previous proposals and may help us to look for new high temperature superconductors using accurate many-body electronic structure tools such as dynamical mean field theory and Green's function based GW method. Similar strategy may be useful for rational digital design of other functional materials such as high thermoelectricity.