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arXiv 1707.07348cond-mat.supr-con
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超导Weyl金属的Larkin-Ovchinnikov态：$\it{\textbf{k}}$ -空间中限制和扩展对的基本区别

Larkin-Ovchinnikov state of superconducting Weyl metals: Fundamental differences between pairings restricted and extended in the $\it{\textbf{k}}$-space

Lei Hao, Rui Wang, Pavan Hosur, C. S. Ting

备注：
27 pages, 11 figures
发表信息：
Phys. Rev. B 96, 094530 (2017)
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摘要：

从理论上研究超导体性质的两种常用方法，在应用于外尔金属的拉金-奥夫钦尼科夫态时，表现出明显的差别。在第一种方法中，配对项被限制在费米面附近的截止能量，而在第二种方法中，配对项被扩展到整个布里渊区。我们通过考虑外尔金属的两个极小模型来探讨它们的区别。对于一个模型，给出了一个单一的外尔口袋对，这两种方法都给出了一个部分缺口（完全缺口）小（大）配对振幅的整体光谱。然而，对于非常小的截止能量，费米表面的一部分可以完全不受第一种方法中的配对项的影响。对于另一个模型给出两对Weyl口袋，而第一种方法的体光谱可以完全间隙，从第二种方法的一个具有强大的线节点，和表面状态也定性地改变了配对。通过拓扑论证和解析分析，我们阐明了上述差异。两种模型的共同因素是外尔锥的倾斜，这导致相对于外尔节点的不对称正常态能带结构。对于具有两对Weyl口袋的Weyl金属，能带折叠导致有效模型中的双重简并，这将第二种方法的配对与所有其他方法区分开来。

英文摘要：

Two common approaches of studying theoretically the property of a superconductor are shown to have significant differences, when they are applied to the Larkin-Ovchinnikov state of Weyl metals. In the first approach the pairing term is restricted by a cutoff energy to the neighborhood of the Fermi surface, whereas in the second approach the pairing term is extended to the whole Brillouin zone. We explore their difference by considering two minimal models for the Weyl metal. For a model giving a single pair of Weyl pockets, both two approaches give a partly-gapped (fully-gapped) bulk spectrum for small (large) pairing amplitude. However, for very small cutoff energy, a portion of the Fermi surface can be completely unaffected by the pairing term in the first approach. For the other model giving two pairs of Weyl pockets, while the bulk spectrum for the first approach can be fully gapped, the one from the second approach has a robust line node, and the surface states are also changed qualitatively by the pairing. We elucidate the above differences by topological arguments and analytical analyses. A factor common to both of the two models is the tilting of the Weyl cones which leads to asymmetric normal state band structure with respect to the Weyl nodes. For the Weyl metal with two pairs of Weyl pockets, the band folding leads to a double degeneracy in the effective model, which distinguishes the pairing of the second approach from all others.

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