Gradient expansion for a spiral phase in a spin-fermion model |
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Authors: | S. Klee A. Muramatsu |
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Affiliation: | (1) Physikalisches Institut der Universität Würzburg, Am Hubland, W-8700 Würzburg, Germany;(2) Physikalisches Institut der Universität Bayreuth, W-8580 Bayreuth, Germany |
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Abstract: | Starting from a doped spin-fermion model for high-temperature superconductors, we derive an effective continuum theory for the spin degrees of freedom by means of a gradient expansion around a spiral spin configuration. By integrating out the fermions in a path-integral representation, we obtain an effective spin-action. An incommensurate, planar spiral configuration for the spin-background is assumed. The long-wavelength limit is obtained by expanding the effective action in powers of a short distance cutoff. The occurring infinite series can be summed to all orders of the coupling constant by exploiting the constraint that the order parameter lives on a circleS1. It is shown that the low-energy limit of the effective action can be mapped onto a O(2) nonlinear model and an additional term due to parity breaking. |
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Keywords: | 74.20.Mn 11.10.Lm 75.10.Jm |
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