Superconductivity at the onset of spin-density-wave order in a metal

Yuxuan Wang, Andrey V. Chubukov

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33 Scopus citations

Abstract

We revisit the issue of superconductivity at the quantum-critical point (QCP) between a 2D paramagnet and a spin-density-wave metal with ordering momentum (π, π). This problem is highly nontrivial because the system at criticality displays a non-Fermi-liquid behavior and because the effective coupling constant λ for the pairing is generally of order one, even when the actual interaction is smaller than fermionic bandwidth. Previous study has found that the renormalizations of the pairing vertex are stronger than in BCS theory and hold in powers of logâ¡2(1/T). We analyze the full gap equation and argue that summing up of the leading logarithms does not lead to a pairing instability. Yet, we show that superconductivity has no threshold and appears even if λ is set to be small, because subleading logarithmical renormalizations diverge and give rise to a BCS-like result logâ¡1/Tcâ̂1/λ. We argue that the analogy with BCS is not accidental as at small λ superconductivity at a QCP predominantly comes from fermions that retain Fermi-liquid behavior at criticality. We compute Tc for the actual λ∼O(1), and find that both Fermi-liquid and non-Fermi-liquid fermions contribute to the pairing.

Original languageEnglish (US)
Article number127001
JournalPhysical review letters
Volume110
Issue number12
DOIs
StatePublished - Mar 20 2013

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