1301.6342 (Jiangping Hu)
Jiangping Hu
Conventionally, parity is even in a superconducting state with spin singlet pairing. However, iron-based superconductors are special systems where spin-singlet pairing states with both even and odd parity can exist because of intrinsic 2-Fe unit cell. The pairing channel with odd parity can be viewed as an extended $\eta$-pairing studied earlier in the Hubbard model. We argue that the extended $A_{1g}$ s-wave and the $\eta$-pairing $B_{2u}$ d-wave are only two possible candidates for iron-based superconductors. The latter should be favored in the presence of strong electron-electron correlation and has a fingerprint with a real space sign inversion between the top and bottom As/Se layers, which has been described as the B-phase in a recently proposed effective $S_4$ model. Ignoring the $\eta$-pairing channel is a fundamental mistake in many previous theoretical studies based on effective models with an 1-Fe unit cell. The existence of the $\eta$-pairing state can pave the way to settle the superconducting mechanism for high temperature superconductors.
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http://arxiv.org/abs/1301.6342
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