861 research outputs found

    Superconductivity and Spin Fluctuations

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    The organizers of the Memorial Session for Herman Rietschel asked that I review some of the history of the interplay of superconductivity and spin fluctuations. Initially, Berk and Schrieffer showed how paramagnon spin fluctuations could suppress superconductivity in nearly-ferromagnetic materials. Following this, Rietschel and various co-workers wrote a number of papers in which they investigated the role of spin fluctuations in reducing the T_c of various electron-phonon superconductors. Paramagnon spin fluctuations are also believed to provide the p-wave pairing mechanism responsible for the superfluid phases of 3He^3He. More recently, antiferromagnetic spin fluctuations have been proposed as the mechanism for d-wave pairing in the heavy-fermion superconductors and in some organic materials as well as possibly the high T_c cuprates. Here I will review some of this early history and discuss some of the things we have learned more recently from numerical simulations.Comment: 9 pages, 10 encapsulated figures, Presented at MOS99, International Conference on Physics and Chemistry of Molecular and Oxide Superconductors, Stockholm, Sweden, 28 July-2 Aug, 1999, corrected typo

    Determining the structure of the superconducting gap in Cu_{2}O_{3} 2-leg ladder materials

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    Superconductivity has been recently observed in Sr_{0.4}Ca_{13.6}Cu_{24}O_{41.84} which contains quasi-one-dimensional Cu_{2}O_{3} 2-leg ladders. If, as suggested by some theories, the superconductivity arises from these 2-leg ladders, it will be important to determine the structure of the superconducting gap. In particular, does the gap in a 2-leg ladder change sign when one goes from the bonding to antibonding fermi surface points? Here we carry out phenomenological calculations of nuclear relaxation rates and inelastic neutron scattering intensity in order to provide estimates of the experimental resolution that will be required to determine the structure of the superconducting gap associated with an array of weakly coupled 2-leg ladders.Comment: 12 pages including 7 eps figures, uses revtex with eps

    Neutron scattering as a probe of the Fe-pnicitide superconducting gap

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    Inelastic neutron scattering provides a probe for studying the spin and momentum structure of the superconducting gap. Here, using a two-orbital model for the Fe-pnicitide superconductors and an RPA-BCS approximation for the dynamic spin susceptibility, we explore the scattering response for various gaps that have been proposed.Comment: 5 pages, 4 figure

    d_{x^2-y^2} Pair Domain Walls

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    Using the density matrix renormalization group, we study domain wall structures in the t-J model at a hole doping of x=1/8. We find that the domain walls are composed of d_{x^2-y^2} pairs and that the regions between the domain walls have antiferromagnetic correlations that are pi phase shifted across a domain wall. At x=1/8, the hole filling corresponds to one hole per two domain wall unit cells. When the pairs in a domain wall are pinned by an external field, the d_{x^2-y^2} pairing response is suppressed, but when the pinning is weakened, d_{x^2-y^2} pair-field correlations can develop.Comment: 11 pages, with 3 Postscript figure