Effective interactions and fluctuation effects in spin-singlet superfluids

Andreas Eberlein and Walter Metzner
Phys. Rev. B 87, 174523 – Published 28 May 2013

Abstract

We derive and evaluate one-loop functional flow equations for the effective interactions, self-energy, and gap function in spin-singlet superfluids. The flow is generated by a fermionic frequency cutoff, which is supplemented by an external pairing field to treat divergencies associated with the Goldstone boson. To parametrize the singular momentum and frequency dependencies of the effective interactions, the Nambu interaction vertex is decomposed in charge, magnetic, and normal and anomalous pairing channels. The one-loop flow solves reduced (mean-field) models for superfluidity exactly, and captures also important fluctuation effects. The Ward identity from charge conservation is generally violated, but can be enforced by projecting the flow. Applying the general formalism to the two-dimensional attractive Hubbard model, we obtain detailed results on the momentum and frequency dependencies of the effective interactions for weak and moderate bare interactions. The gap is reduced by fluctuations, with a stronger reduction at weaker interactions, as expected.

  • Received 7 February 2013

DOI:https://doi.org/10.1103/PhysRevB.87.174523

©2013 American Physical Society

Authors & Affiliations

Andreas Eberlein and Walter Metzner

  • Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany

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Issue

Vol. 87, Iss. 17 — 1 May 2013

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