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arXiv · 0704.0241

Superconducting states of the quasi-2D Holstein model: Effects of vertex and non-local corrections

J. P. Hague
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Abstract

I investigate superconducting states in a quasi-2D Holstein model using the dynamical cluster approximation (DCA). The effects of spatial fluctuations (non-local corrections) are examined and approximations neglecting and incorporating lowest-order vertex corrections are computed. The approximation is expected to be valid for electron-phonon couplings of less than the bandwidth. The phase diagram and superconducting order parameter are calculated. Effects which can only be attributed to theories beyond Migdal--Eliashberg theory are present. In particular, the order parameter shows momentum dependence on the Fermi-surface with a modulated form and s-wave order is suppressed at half-filling. The results are discussed in relation to Hohenberg's theorem and the BCS approximation.

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J. P. Hague. 2007-04-02. Superconducting states of the quasi-2D Holstein model: Effects of vertex and non-local corrections. https://doi.org/10.1088/0953-8984%2F17%2F37%2F005

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