在过去的二十年里，单原子层的生长和剥落取得了突破性进展，开创了科学发现和技术创新的新时代。 继石墨烯之后，过渡金属硫族化合物（**s）受到广泛关注，成为许多新颖量子现象的宝库。 近年来，在NBSE2等材料中观察到了一种称为ising超导性的现象，这种现象主要由自旋轨道耦合和中心反转对称性破坏驱动。
fig. 1 electron–phonon interaction and intra/inter-pocket eliashberg spectral function.
超导体与其他层状材料（如拓扑材料、单层和二维磁性层状材料）之间的邻近性和界面效应有望应用于量子信息存储和自旋电子学器件。 近年来，除了占主导地位的电声耦合（EPC）外，人们还关注了自旋涨落（SF）在超导现象中可能的作用，讨论了三重态占主导地位的可能性，并提出了关于单重态-三重态Leggett振荡的猜想。 然而，这些假设尚未经过定量检验。
fig. 2 superconducting gap without and with spin-fluctuation interaction.
美国弗吉尼亚州乔治梅森大学物理与天文学系DAS等人基于第一性原理计算，对伊辛超导体NBSE2进行了详细研究，确定了EPC和SF的作用。 作者发现：（1）EPC具有较强的各向异性，主要来自k-k'散射，从而排除了三重态对称性作为激发态的可能性;（2）超导性被SF显著减弱，但各向异性保持不变。 （3）作者发现了Leggett模式的可能性，不是在单重态-三重态之间，而是在S++ S通道中。
fig. 3 schematic illustration of the ising superconductor pairing symmetry.
通过对电声耦合和自旋涨落贡献的自洽分析，估算了平均BCS能隙δBCS、Leggett模频L和L 2δBCS，与实验结果相近。 本研究为理解NBSE2等超导体的超导现象提供了全面的定量分析，为今后的实验和理论研究提供了有力的支持。 相关新闻**最近发表在NPJ Computational Materials上
fig. 4 analytical solution of the two-gap bcs equations.
editorial summary
unr**eling the ising superconductivity in nbse2: electron-phonon coupling and spin fluctuations
revolutionary progress in the growth and exfoliation of single atomic layers over the last two decades has led to a new era of scientific discoveries and technological innovation. following graphene, transition metal dichalcogenides (*s) h**e taken the spotlight, as a treasure trove for a plethora of novel quantum phenomena. in recent years, a phenomenon called ising superconductivity has been observed in materials such as nbse2, driven primarily by spin-orbit coupling and the absence of inversion symmetry. the proximity and interface effects between ising superconductors and other layered materials, such as topological materials, single-layer **s, and two-dimensional magnetic layered materials, could lead to interesting device applications for quantum information storage and spintronics. recently, attention was called to the possible role that spin fluctuations (sf) play in this phenomenon, in addition to the dominant electron–phonon coupling (epc); the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet leggett oscillations. however, these hypotheses h**e not been put to a quantitative test.
s. das et al. from the department of physics and astronomy, george mason university, usa, conducted an in-depth study on the ising superconductor nbse2, and explored the roles of epc and sf based on first-principles calculations. the authors found that: (1) epc is strongly anisotropic, largely coming from the k−k’ scattering, and therefore excludes triplet symmetry even as an excited state; (2) superconductivity is substantially weakened by sf, but anisotropy remains as above; and, (3) the possibility of a leggett mode was found, not in a singlet–triplet but in an s++ s± channel. based on the self-consistent analytical solution and first-principles calculations including electron–phonon coupling and spin-fluctuation contribution, the authors estimated the **erage bcs gap δbcs, leggett mode frequency ωl, and the ratio ωl/2δbcs, showing good agreement with experimental results. this study provides a fairly comprehensive quantitative analysis for understanding the superconductivity in nbse2 and other ising superconductors, offering valuable insights for future experimental and theoretical research.thisarticle was recently published in npj computational materials
原文摘要及其译文
ISING超导体Nbse2中的电子-声子耦合和自旋涨落
s. das, h. paudyal, e. r. margine, d. f. agterberg & i. i. mazin
abstract
ising superconductivity, observed in nbse2 and similar materials, has generated tremendous interest. recently, attention was called to the possible role that spin fluctuations (sf) play in this phenomenon, in addition to the dominant electron–phonon coupling (epc); the possibility of a predominantly triplet state was discussed and led to a conjecture of viable singlet–triplet leggett oscillations. however, these hypotheses h**e not been put to a quantitative test. in this **we report first principle calculations of the epc and also estimate coupling with sf, including full momentum dependence. we find that: (1) epc is strongly anisotropic, largely coming from the k−k′ scattering, and therefore excludes triplet symmetry even as an excited state; (2) superconductivity is substantially weakened by sf, but anisotropy remains as above; and, (3) we do find the possibility of a leggett mode, not in a singlet–triplet but in an s++ s±channel.
总结：
在NBSE2和类似材料中观察到的超导性非常值得关注。 最近，除了占主导地位的电声耦合（EPC）之外，人们还关注了自旋涨落（SFs）在这一现象中可能的作用，讨论了三重态占主导地位的可能性，并提出了关于单重态-三重态Leggett振荡的猜想。 然而，这些假设尚未经过定量检验。 在本文中，我们报告了电声耦合的第一性原理计算，并估计了与自旋涨落的耦合，包括全动量依赖性。 结果表明：（1）EPC具有很强的各向异性，主要来自k-k'散射，因此即使作为激发态，三重态对称性也被排除在外;（2）超导性因自旋涨落而明显减弱，但各向异性仍然存在。 （3） 我们确实发现了 leggett 模式的可能性，不是在单重态-三重态之间，而是在 S++ S 通道中。