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Spin fluctuations and superconductivity in a three-dimensional tight-binding model for BaFe_2As_2

机译：BaFe_2As_2的三维紧密结合模型中的自旋涨落和超导

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摘要

Despite the wealth of experimental data on the Fe-pnictide compounds of the KTe_2As_2 type, K=Ba, Ca, or Sr, the main theoretical work based on multiorbital tight-binding models has been restricted so far to the study of the related 1111 compounds. This can be ascribed to the more three-dimensional electronic structure found by ab initio calculations for the 122 materials, making this system less amenable to model development. In addition, the more complicated Brillouin zone (BZ) of the body-centered tetragonal symmetry does not allow a straightforward unfolding of the electronic band structure into an effective 1Fe/unit cell BZ. Here we present an effective five-orbital tight-binding fit of the full density functional theory band structure for BaFe_2As_2 including the k_z dispersions. We compare the five-orbital spin fluctuation model to one previously studied for LaOFeAs and calculate the random-phase approximation enhanced susceptibility. Using the fluctuation exchange approximation to determine the leading pairing instability, we then examine the differences between a strictly two-dimensional model calculation over a single kz cut of the BZ and a completely three-dimensional approach. We find pairing states quite similar to the 1111 materials, with generic quasi-isotropic pairing on the hole sheets and nodal states on the electron sheets at k_z=0, which however are gapped as the system is hole doped. On the other hand, a substantial k_z dependence of the order parameter remains, with most of the pairing strength deriving from processes near k_z=π. These states exhibit a tendency for an enhanced anisotropy on the hole sheets and a reduced anisotropy on the electron sheets near the top of the BZ.
机译：尽管有大量关于KTe_2As_2型，K = Ba，Ca或Sr的Fe锡化合物的实验数据，但迄今为止，基于多轨道紧密结合模型的主要理论工作仅限于相关1111化合物的研究。这可以归因于从头计算对122种材料发现的三维电子结构，从而使该系统不太适合模型开发。另外，以身体为中心的四边形对称性的更复杂的布里渊区（BZ）不允许将电子带结构直接展开为有效的1Fe /单位单元BZ。在这里，我们提出了BaFe_2As_2包括k_z色散的全密度泛函理论能带结构的有效五轨道紧密结合拟合。我们将五轨道自旋涨落模型与先前研究的LaOFeAs模型进行了比较，并计算了随机相位近似增强的磁化率。使用涨落交换近似法确定前导配对不稳定性，然后我们研究了BZ的单个kz切割上的严格二维模型计算与完全三维方法之间的差异。我们发现配对状态与1111材料非常相似，在空穴板上具有通用的准各向同性配对，在电子薄片上的k_z = 0处具有节点态，但是由于系统掺杂了空穴，因此它们之间存在间隙。另一方面，阶参数的基本k_z依赖性仍然存在，大部分配对强度来自k_z =π附近的过程。这些状态显示出在BZ顶部附近的空穴板上的各向异性增强和在电子板上的各向异性减小的趋势。

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  • 来源
    《Physical review》 |2010年第21期|P.214503.1-214503.12|共12页
  • 作者

    S. Graser; A. F. Kemper; T. A. Maier; H.-P. Cheng; P. J. Hirschfeld; D. J. Scalapino;

  • 作者单位

    Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, D-86135 Augsburg, Germany;

    rnDepartment of Physics, University of Florida, Gainesville, Florida 32611, USA;

    Center for Nanophase Materials Sciences and Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6494, USA;

    rnDepartment of Physics, University of Florida, Gainesville, Florida 32611, USA;

    Department of Physics, University of Florida, Gainesville, Florida 32611, USA;

    Department of Physics, University of California, Santa Barbara, California 93106-9530, USA;

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  • 关键词

    pairing symmetries (other than s-wave);

    机译：配对对称（s波除外）;

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