Vortex core states in a minimal two-band model for iron-based superconductors

Abstract

The pairing symmetry is one of the major issues in the study of iron-based superconductors. We adopt a minimal two-band tight-binding model with various channels of pairing interaction, and derive a set of two-band Bogoliubov–de Gennes (BdG) equations. The BdG equations are implemented in real space and then solved self-consistently via exact diagonalization. In the uniform case, we find that the dx2−y2-wave pairing state is most favorable for a nearest-neighbor pairing interaction while the sx2y2-wave pairing state is most favorable for a next-nearest-neighbor pairing interaction, which is consistent with that reported by Seo et al. [Phys. Rev. Lett. 101, 206404 (2008)]. We then proceed to study the local electronic structure around a magnetic vortex core for both dx2−y2-wave and sx2y2-wave pairing symmetry in the mixed state. It is found from the local density of states spectra and its spatial variation that the resonance core states near the Fermi energy for the dx2−y2-wave pairing symmetry are bound while those for the sx2y2-wave pairing symmetry can evolve from the localized states into extended ones with varying electron filling factor. Furthermore, by including an effective exchange interaction, the emergent antiferromagnetic spin-density-wave order can suppress the resonance core states, which provides one possible avenue to understand the absence of resonance peak as revealed by recent scanning tunneling microscopy experiment by Yin et al. [Phys. Rev. Lett. 102, 097002 (2009)].

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