Valley density-wave and multiband superconductivity in iron-based pnictide superconductors

Abstract

The key feature of the Fe-based superconductors is their quasi-two-dimensional 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 wave vector 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 nonuniform “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.

Source-reported materials — not catalogue approval

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