Condensed Matter Seminar Announcement Prof. Ross McKenzie University of Queensland (Brisbane, Australia) " Interplay of unconventional superconductivity and frustrated antiferromagnetism in layered organic molecular crystals " Date: Thursday, March 17, 2005 Time: 4:10 pm 416 Physics Abstract: There are more than one hundred charge transfer salts of the composition D2X, where D is an organic donor molecule (such as BEDT-TTF) and X is an anion, which have quasi-two-dimensional electronic and magnetic properties. They exhibit a rich phase diagram as a function of temperature, pressure, anion X, and magnetic field. There is subtle competition between antiferromagnetic, insulating, Fermi liquid, bad metal, and unconventional superconducting phases. A minimal strongly correlated electron model to describe a broad class of these materials is a Hubbard model on an anisotropic triangular lattice at half filling. The frustrated antiferromagnetic correlations are key to understanding these materials. It has been recently shown that some of the key physics can be described by a Resonating Valence Bond (RVB) variational wave function for the relevant Hubbard-Heisenberg model. This theory explains the first order phase transition from a Mott insulator to a d-wave superconductor, the pseudogap, and the small superfluid density. This work underscores the similarity of these organic superconductors to the cuprate superconductors. References: B.J. Powell and R.H. McKenzie, Phys. Rev. Lett. 94, 047004 (2005). W. Zheng et al., cond-mat/0410381

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