Condensed Matter Seminar: "Computational studies of iron-based high critical temperature superconductors"

Thursday, September 7, 2017 - 11:30am

Elbio R. A. Dagotto (University of Tennessee and ORNL)

Fermi surface nesting guided the initial theoretical studies of iron-based high critical temperature superconductors but evidence is accumulating that these materials are more complex than previously anticipated. For example, competition between antiferromagnetic and ferromagnetic tendencies leads to frustration and unusual magnetic states. In this framework, two areas of research that are receiving considerable attention will be addressed:(a) The two-leg ladder compound BaFe2S3 is the only member of the iron-based family that becomes superconducting (at high pressure) without having iron layers in its crystal structure. Recent theoretical results using the density matrix renormalization group for a two-orbital Hubbard model applied to both ladders and chains will be discussed. They correctly reproduce the dominant magnetic order and have revealed intriguing indications of pairing tendencies at intermediate/strong couplings upon doping. Results for the dynamical spin structure factor of ladders and other time dependent effects such as sudden expansions will be briefly addressed.(b) Time allowing, the exotic spin nematic regime of iron superconductors will be discussed from the perspective of spin-fermion model simulations. Recent efforts include the influence of quenched disorder and the case of FeTe where coupling electrons to a monoclinic lattice distortion reproduces the bicollinear magnetic order and "reversed" resistivity anisotropy found experimentally.

Physics 298

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