A generic two-band model for unconventional superconductivity and spin-density-wave order in electron- and hole-doped iron-based superconductorsQ. Han1, Y. Chen2 and Z. D. Wang3
1 Department of Physics, Renmin University - Beijing, China
2 Department of Physics and Lab of Advanced Materials, Fudan University - Shanghai, China
3 Department of Physics and Center of Theoretical and Computational Physics, The University of Hong Kong Pokfulam Road, Hong Kong, China
received 8 April 2008; accepted in final form 14 April 2008; published May 2008
published online 23 April 2008
Based on experimental data on the newly synthesized iron-based superconductors and the relevant band structure calculations, we propose a minimal two-band BCS-type Hamiltonian with the interband Hubbard interaction included. We illustrate that this two-band model is able to capture the essential features of unconventional superconductivity and spin-density-wave (SDW) ordering in this family of materials. It is found that bound electron-hole pairs can be condensed to reveal the SDW ordering for zero and very small doping, while the superconducting ordering emerges at small finite doping, whose pairing symmetry is qualitatively analyzed to be of nodal d-wave. The derived analytical formulas not only give out a nearly symmetric phase diagram for electron and hole doping, but also are likely able to account for existing main experimental results. Moreover, we also derive two important relations for a general two-band model and elaborate how to apply them to determine the band width ratio and the effective interband coupling strength from experimental data.
74.20.-z - Theories and models of superconducting state.
75.30.Fv - Spin-density waves.
74.25.-q - Properties of type I and type II superconductors.
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