在過去的二十年裡，單原子層的生長和剝落取得了突破性進展，開創了科學發現和技術創新的新時代。 繼石墨烯之後，過渡金屬硫族化合物（**s）受到廣泛關注，成為許多新穎量子現象的寶庫。 近年來，在NBSE2等材料中觀察到了一種稱為ising超導性的現象，這種現象主要由自旋軌道耦合和中心反轉對稱性破壞驅動。
fig. 1 electron–phonon interaction and intra/inter-pocket eliashberg spectral function.
超導體與其他層狀材料（如拓撲材料、單層和二維磁性層狀材料）之間的鄰近性和介面效應有望應用於量子資訊儲存和自旋電子學器件。 近年來，除了佔主導地位的電聲耦合（EPC）外，人們還關注了自旋漲落（SF）在超導現象中可能的作用，討論了三重態佔主導地位的可能性，並提出了關於單重態-三重態Leggett振盪的猜想。 然而，這些假設尚未經過定量檢驗。
fig. 2 superconducting gap without and with spin-fluctuation interaction.
美國維吉尼亞州喬治梅森大學物理與天文學系DAS等人基於第一性原理計算，對伊辛超導體NBSE2進行了詳細研究，確定了EPC和SF的作用。 作者發現：（1）EPC具有較強的各向異性，主要來自k-k'散射，從而排除了三重態對稱性作為激發態的可能性;（2）超導性被SF顯著減弱，但各向異性保持不變。 （3）作者發現了Leggett模式的可能性，不是在單重態-三重態之間，而是在S++ S通道中。
fig. 3 schematic illustration of the ising superconductor pairing symmetry.
通過對電聲耦合和自旋漲落貢獻的自洽分析，估算了平均BCS能隙δBCS、Leggett模頻L和L 2δBCS，與實驗結果相近。 本研究為理解NBSE2等超導體的超導現象提供了全面的定量分析，為今後的實驗和理論研究提供了有力的支援。 相關新聞**最近發表在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
原文摘要及其譯文
ISING超導體Nbse2中的電子-聲子耦合和自旋漲落
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.
總結：
在NBSE2和類似材料中觀察到的超導性非常值得關注。 最近，除了佔主導地位的電聲耦合（EPC）之外，人們還關注了自旋漲落（SFs）在這一現象中可能的作用，討論了三重態佔主導地位的可能性，並提出了關於單重態-三重態Leggett振盪的猜想。 然而，這些假設尚未經過定量檢驗。 在本文中，我們報告了電聲耦合的第一性原理計算，並估計了與自旋漲落的耦合，包括全動量依賴性。 結果表明：（1）EPC具有很強的各向異性，主要來自k-k'散射，因此即使作為激發態，三重態對稱性也被排除在外;（2）超導性因自旋漲落而明顯減弱，但各向異性仍然存在。 （3） 我們確實發現了 leggett 模式的可能性，不是在單重態-三重態之間，而是在 S++ S 通道中。