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arXiv 0905.0014cond-mat.supr-concond-mat.str-el
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铁基超导体最小双带模型中的涡旋芯态

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

Xiang Hu, C. S. Ting, Jian-Xin Zhu

摘要:

对对称性是铁基超导体研究中的主要问题之一。我们采用一个最小的双带紧束缚模型,考虑了不同的配对作用通道,导出了一组双带Bogoliubov-de Gennes(BdG)方程。BdG方程在实空间中实现,然后通过精确对角化自洽求解。在均匀情况下,我们发现$d_{x^2-y^2}$波配对态最有利于最近邻配对相互作用,而$s_{x^2y^2}$波配对态最有利于次最近邻配对相互作用.这与Seo { \em et al.}报道的结果一致。[Phys. Rev. Lett. { \bf 101},206404(2008)]。然后,我们继续研究的局部电子结构周围的磁涡旋核心的$d_{x^2-y^2}$波和$s_{x^2y^2}$波配对对称的混合状态。从局域态密度(LDOS)谱及其空间变化发现,对于$d_{x^2-y^2}$波对对称,费米能附近的共振芯态是束缚态,而对于$s_{x^2y^2}$波对对称,随着电子填充因子的变化,共振芯态可以从局域态演化到扩展态.此外,通过包括有效的交换相互作用,出现的反铁磁自旋密度波(SDW)序可以抑制共振芯态,这为理解Yin { \em et al.}最近的扫描隧道显微镜实验(STM)所揭示的共振峰的缺失提供了一种可能的途径。[Phys. Rev. Lett. { \bf 102},097002(2009)]。

英文摘要:

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 $d_{x^2-y^2}$-wave pairing state is most favorable for a nearest-neighbor pairing interaction while the $s_{x^2y^2}$-wave pairing state is most favorable for a next-nearest-neighbor pairing interaction. The is consistent with that reported by Seo {\em et al.} [Phys. Rev. Lett. {\bf 101}, 206404 (2008)]. We then proceed to study the local electronic structure around a magnetic vortex core for both $d_{x^2-y^2}$-wave and $s_{x^2y^2}$-wave pairing symmetry in the mixed state. It is found from the local density of states (LDOS) spectra and its spatial variation that the resonance core states near the Fermi energy for the $d_{x^2-y^2}$-wave pairing symmetry are bound while those for the $s_{x^2y^2}$-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 (SDW) 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 (STM) by Yin {\em et al.} [Phys. Rev. Lett. {\bf 102}, 097002 (2009)].

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