Sensitivity of the superconducting transition temperature to changes in the spin-fluctuation spectral weight

Abstract

In the simplest model of magnetic pairing, the transition temperature to the superconducting state depends on the dynamical susceptibility χ(q,ω). We discuss how Tc is affected by different momentum and frequency parts of χ(q,ω) for nearly antiferromagnetic and nearly ferromagnetic metals in two dimensions on a square lattice. For a wide range of model parameters, we map out the regions in momentum and frequency which lead to either a suppression or enhancement of Tc. We find a comparatively large region in frequency and momentum space around the incipient ordering wave vector at which the addition of spin-fluctuation spectral weight leads to an increase in Tc. This suggests that, in the range of parameters studied, pairing occurs mostly through the short-range magnetic fluctuations. When spectral weight is added at momentum transfers diagonally opposite the incipient ordering wave vector, near q=(0,0) for nearly antiferromagnetic or near q=(π,π) for nearly ferromagnetic systems, spin fluctuations are always pair breaking. We note how this feature partially explains the paucity of examples of superconductivity on the border of itinerant ferromagnetism. In agreement with previous work, we find that low-frequency spin fluctuations lead to a suppression of Tc in nearly antiferromagnetic metals and find that this is also true in the case of ferromagnetic spin fluctuations. We show that the frequency at which the spin fluctuations cross over from pair breaking to pair forming depends relatively weakly on the effective interaction constants.

Source-reported materials — not catalogue approval

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