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TT: Fachverband Tiefe Temperaturen

TT 68: Superconductivity: Fe-based Superconductors - Theory I

TT 68.1: Hauptvortrag

Mittwoch, 2. April 2014, 15:00–15:30, HSZ 201

Novel Effects of Disorder in Multiband Unconventional Superconductors — •Peter J Hirschfeld — Phys. Dept.. U. Florida, Gainesville FL 32611, USA — Institut für Theoretische Physik, Goethe-Universität Frankfurt, 60438 Frankfurt am Main

Impurities been studied in superconductors for many years because, depending on the type of impurity and on the symmetry of the superconducting state, they may break Cooper pairs. They thus play an important diagnostic role in deducing the type of superconductivity one has in a newly discovered material. I focus here on the Fe-based superconductors, which are multiband in character and probably exhibit unconventional pairing states, including so-called "s+/-" states which change sign of the order parameter between bands. Impurity scattering in such states depends sensitively on the ratio of intra- to interband scattering, giving rise to novel effects of disorder, including possible transitions to conventional "s++" states and lifting of gap nodes. I propose that one can uniquely identify an s+/- state by a sequence of transitions with controlled disorder, observable in bulk quasiparticle transport or NMR. I next focus on STM experiments, and the inability of current lattice-based theories to capture not only the fine structure of STM conductance maps, but also certain local symmetries. I propose to remedy this by using a Wannier-function based extension of the BdG equations of inhomogenous superconductivity. Finally, I discuss the role of correlations in creating C4 symmetry-broken emergent defect states, which may have important consequences for the ubiquitous electronic nematicity observed in these materials.