Perturbation Theory of High-Tc Superconductivity in Iron Pnictides
Perturbation Theory of High-Tc Superconductivity in Iron Pnictides
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DOI：
10.1143/jpsj.78.034716
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发表时间：
2008-11
期刊：
影响因子：
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通讯作者：
T. Nomura
中科院分区：
文献类型：
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作者：
T. Nomura
最近在铁磷族化物中发现的高转变温度（高 Tc）超导性在微扰理论中进行了分析。具体来说，通过求解具有真实电子结构的多能带（2 和 5 能带）哈伯德模型的 Eliashberg 方程，研究了可能的配对对称性、转变温度的掺杂依赖性和配对机制。有效配对相互作用在现场库仑积分中微扰地扩展到三阶。我们的微扰弱耦合方法表明，通过在 5 带模型中采用实际的现场库仑积分，可以获得足够大的 Eliashberg 方程特征值来解释实际的高转变温度。因此，非常规（非声子介导）超导性很有可能实现。超导有序参数在费米面上不会改变其符号，但在电子和空穴费米面之间会发生变化。因此，在我们研究的整个参数区域中，可能的配对对称性始终是“无节点扩展 s 波对称性（更具体地说，s_{+-} 波对称性）”。这表明 2 频带模型不足以解释 Tc 的高值。
The high-transition-temperature (high-Tc) superconductivity discovered recently in iron pnictides is analyzed within a perturbation theory. Specifically, the probable pairing symmetry, the doping dependence of the transition temperature and the pairing mechanism are studied by solving the Eliashberg equation for multi-band (2- and 5-band) Hubbard models with realistic electronic structures. The effective pairing interaction is expanded perturbatively in the on-site Coulomb integrals up to third order. Our perturbative weak-coupling approach shows that sufficiently large eigenvalues of the Eliashberg equation are obtained to explain the actual high transition temperatures by taking realistic on-site Coulomb integrals in the 5-band model. Thus, unconventional (non-phonon-mediated) superconductivity is highly likely to be realized. The superconducting order parameter does not change its sign on the Fermi surfaces, but it does change between the electron and hole Fermi surfaces. Consequently, the probable pairing symmetry is always "a nodeless extended s-wave symmetry (more specifically, an s_{+-}-wave symmetry)" over the whole parameter region that we investigated. It is suggested that the 2-band model is insufficient to explain the high values of Tc.