Electronic Structure and Superconducting Gap Structure in BiS2-based Layered Superconductors
Electronic Structure and Superconducting Gap Structure in BiS2-based Layered Superconductors
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DOI：
10.7566/jpsj.88.041008
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发表时间：
2019-04-15
影响因子：
1.7
通讯作者：
Ikeda, Hiroaki
中科院分区：
文献类型：
--
作者：
Suzuki, Katsuhiro;Usui, Hidetomo;Ikeda, Hiroaki
基于bis2的层状超导体由于铋6p轨道相对较大的自旋-轨道耦合，非谐波声子的强耦合性质以及一些各向异性超导间隙结构的证据而引起了相当大的兴趣。在研究初期，对传统的电子-声子机制和非常规的电子-声子机制进行了超导配对机制的研究。大多数实验结果可以用全间隙强耦合s波态很好地解释，这是由电子-声子相互作用驱动的。然而，最近的角分辨光发射测量表明，超导间隙有可能发生明显变化。此外，同位素效应的不存在也有报道。这些最近的发现与传统的s波配对状态不一致，而是暗示了非常规的配对状态。这意味着配对胶也仍然不清楚。在这篇综述文章中，我们概述了晶体结构，电子带结构，声子性质，以及这些超导体中超导间隙结构/配对机制的候选材料。我们还讨论了由纯吸引相互作用驱动的节点间隙结构的可能性。
BiS2-based layered superconductors have attracted considerable interest owing to the relatively large spin-orbit coupling of bismuth 6p orbitals, the strong coupling nature by anharmonic phonons, and some evidence of an anisotropic superconducting gap structure. In the early stage of study, both conventional electron-phonon and unconventional mechanisms were examined as the superconducting pairing mechanism. Most experimental results can be well explained by the fully gapped strong-coupling s-wave state, which is driven by the electron-phonon interactions. Nevertheless, the recent angle-resolved photoemission measurement has indicated the possibility of a sign change of the superconducting gap. Furthermore, the absence of the isotope effect has been reported. These recent findings are at odds with the conventional s-wave pairing state, and rather imply unconventional pairing states. This means that the pairing glue also remains unclear. In this review article, we provide an overview of the crystal structures, electronic band structures, phonon properties, and candidates for the superconducting gap structures/pairing mechanisms in these superconductors. We also discuss the possibility of a nodal gap structure driven by purely attractive interactions.