Valley density-wave and multiband superconductivity in Fe-pnictides

Abstract

The key feature of the Fe-based superconductors is their quasi 2D multiband Fermi surface. By relating the problem to a negative U Hubbard model and its superconducting ground state, we show that the defining instability of such a Fermi surface is the valley density-wave (VDW), a combined spin/charge density-wave at the wavevector connecting the electron and hole valleys. As the valley parameters change by doping or pressure, the fictitious superconductor experiences "Zeeman splitting", eventually going into a non-uniform "Fulde-Ferrell-Larkin-Ovchinikov" (FFLO) state, an itinerant and often incommensurate VDW of the real world, characterized by the metallic conductivity from the ungapped remnants of the Fermi surface. When "Zeeman splitting" exceeds the "Chandrasekhar-Clogston" limit, the "FFLO" state disappears, and the VDW is destabilized. Near this point, the VDW fluctuations and interband pair repulsion are essential ingredients of high-Tc superconductivity in Fe-pnictides.

8 pages, 2 figures; expanded version; extended discussion; additional references

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Cited by in corpus (4)

• The Structural Phase Transition in FeSe (Fe1+dSe)
• Momentum dependence and nodes of the superconducting gap in iron-pnictides
• Antiferromagnetically Driven Electronic Correlation in Iron Pnictides and Cuprates
• Vortex state in iron-based superconductors with collinear antiferromagnetic cores