In this paper we explore the magnetic and orbital properties closely related to a tetragonal-orthorhombic structural phase transition in iron pnictides based on both two- and five-orbital Hubbard models. The electron-lattice coupling, which interplays with electronic interaction, is self-consistently treated. Our results reveal that the orbital polarization stabilizes the spin density wave (SDW) order in both tetragonal and orthorhombic phases. However, the ferro-orbital density wave (F-ODW) only occurs in the orthorhombic phase rather than in the tetragonal one. Magnetic moments of Fe are small in the intermediate Coulomb interaction region for the striped antiferromangnetic phase in the realistic five orbital model. The anisotropic Fermi surface in the SDW/ODW orthorhombic phase is well in agreement with the recent angle-resolved photoemission spectroscopy experiments. These results suggest a scenario that the magnetic phase transition is driven by the ODW order mainly arising from the electron-lattice coupling.
Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides
在母体和电子掺杂的化合物中，已经广泛地研究了铁磷属元素化物的耦合正交和磁性转变的电阻率的面内各向异性。所有这些研究普遍表明，在低于磁转变温度时自旋沿其反铁磁耦合的长斜方轴$a_{O}$上的电阻率$ρ_{a}$小于短斜方轴$b_{O}$的电阻率$ρ_{b}$，即。e. $ρ_{a}<ρ_{b}$。本文报道了在空穴掺杂化合物Ba $_{1-x}$ K $_{x}$ Fe $_{2}$ As $_{2}$中，随着掺杂量的增加，电阻率各向异性开始变得非常小，当掺杂量足够大时，电阻率各向异性最终改变符号，即：e. $ρ_{b}<ρ_{a}$。这一观察结果与最近的理论预测一致，该理论预测考虑了正交/斜方晶态中自旋波动对电子的各向异性散射。
Reply to Comment on "Violation of Anderson's Theorem for the sign-reversing s-wave state of Iron-Pnictide Superconductors" [arXiv:1012.0414] by Y. Bang
One of the outstanding problems in Iron pnictide research is the unambiguous detection of its pairing symmetry. The most probable candidates are the two-band s$++$ and sign reversed s$\pm$ wave pairing. In this work, the Andreev conductance and shot noise are used as a probe for the pairing symmetry of Iron pnictide superconductors. Clear differences emerge in both the zero bias differential conductance and the shot noise in the tunneling limit for the two cases enabling an effective distinction between the two.
Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory
The phenomenology of the iron pnictide superconductor can be described by the threeband s+- Eliashberg theory in which the mechanism of superconducting coupling is mediated by antiferromagnetic spin fluctuations and whose characteristic energy W0 scales with Tc according to the empirical law W0 = 4.65kBTc. This model presents the universal characteristics that are independent of the critical temperature, such as the link between the two free parameters l13 and l23 and the ratio Di/kBTc.
Orbital Order, Structural Transition and Superconductivity in Iron Pnictides
我们研究了铁磷属元素化物超导体的16带d-p模型，其中存在电子-声子耦合g和正交模，这对于再现最近观察到的超声软化是至关重要的。在RPA中，我们得到了低于TQ的铁轨道序，它在Ts = TQ处诱导四方-正交结构转变，以及低于TN的条纹型反铁磁序。在相变附近，当TQ > TN时，由于轨道涨落，系统表现出s++波超导电性，而当TQ > TN时，由于磁场涨落，系统表现出s+-波超导电< TN. The former case is consistent with the phase diagram of doped iron pnictides with Ts >性.
Comment on "Violation of Anderson's Theorem for the sign-reversing s-wave state of Iron-Pnictide Superconductors" by Onari et al., Phys. Rev. Lett. 103, 177001(2009)[1]
Tracing the $s_\pm$-symmetry in iron pnictides by controlled disorder
连续质子辐照使铁的超导转变温度单调下降。我们对Ba（Fe $_{0.9}$ Co $_{0.1}$）$_2$ As $_2$薄膜的系统光学太赫兹研究揭示，然而，低能超导能隙首先被抑制，但在较高的辐照剂量下恢复。与此同时，超流体密度随无序度的下降也停止了。这些观察结果与理论计算非常吻合，理论计算预测了无序诱导的序参量从$s_{\pm}$到$s_{++}$对称性的转变。因此，我们解决了长期以来的困惑铁pnictides间隙对称性有利于$s_{\pm}$对称性和证明太赫兹光谱作为一种工具，以确定超导序参量的对称性。
Charge doping-induced quasiparticle scattering in iron-pnictide superconductors as probed by vortex pinning
铁磷属元素化物超导体的电荷掺杂导致磁通涡旋的集体钉扎，而等价掺杂则不会。此外，磁通钉扎在电荷掺杂的化合物是一贯的平均自由程波动所引入的掺杂剂原子，允许提取的弹性准粒子散射率。等价掺杂的BaFe $_{2}$（As $_{1-x}$ P $_{x}$）$_{2}$中不存在掺杂剂原子的散射与该材料中低温渗透深度的线性温度依赖性的观察结果一致。
We study Josephson junctions between a multi-band iron-pnictide Ba1-xNaxFe2As2 and conventional s-wave superconductors Nb and Cu/Nb bilayer. We observe that junctions with a Cu interlayer exhibit much larger IcRn, despite a weaker proximity-induced superconductivity. This counterintuitive result is attributed to the difference in Fermi surface geometries of Nb and Cu, which leads to a selective one-band tunneling from Cu and a non-selective multi-band tunnelng from Nb. The latter leads to a mutual cancellation of supercurrents due to the sign-reversal s+- symmetry of the order parameter in the…
Observation of anisotropic diamagnetism above the superconducting transition in iron-pnictide Ba_(1-x)K_xFe2As2 single crystals due to thermodynamic fluctuations
Intergrain Josephson Currents in Multigap Superconductors: Microscopic Origin of Low Intergrain Critical Current and Its Recovery Potential in Iron-Pnictide Materials
Local antiferromagnetic correlations in the iron pnictide superconductors LaFeAsO{1-x}F{x} and Ca(Fe,Co)2As2 as seen via normal-state susceptibility
本文研究了LaFeAsO $_{1-x}$ F $_x$和Ca（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$中磁性和超导电性的相互作用。虽然反铁磁自旋密度波的形成被抑制和超导性的发展，所有的样品显示出掺杂独立的正常状态下的磁化率的加热后，出现了铁磷属元素的一般功能的强烈增加。这些数据提供了证据，强大的本地反铁磁相关坚持即使在超导制度的相图。
The mechanism of formation of dome-like phase diagrams and the features of magnetic field penetration in iron pnictides with hetero- and isovalent doping are considered within the framework of the previously proposed model, which assumes the local character of doping and the cluster structure of resulted superconducting phase. It is shown that the proposed model, despite its simplicity and neglect of the features of the electronic structure, makes it possible not only to accurately calculate the positions of superconducting domes on the phase diagrams of specific HTSC compounds, but also to ex…
