Anisotropic band splitting in monolayer NbSe2: implications for superconductivity and charge density wave
Anisotropic band splitting in monolayer NbSe2: implications for superconductivity and charge density wave
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DOI：
10.1038/s41699-018-0057-3
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发表时间：
2018-05
影响因子：
9.7
通讯作者：
Y. Nakata;K. Sugawara;S. Ichinokura;Y. Okada;T. Hitosugi;T. Koretsune;K. Ueno;S. Hasegawa;Takashi Takahashi;Takafumi Sato
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文献类型：
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作者：
Y. Nakata;K. Sugawara;S. Ichinokura;Y. Okada;T. Hitosugi;T. Koretsune;K. Ueno;S. Hasegawa;Takashi Takahashi;Takafumi Sato
实现二维过渡金属二硫属化合物的非常规物理性质是当前凝聚态系统研究的关键挑战之一。然而，2D TMD的电子性质与其散装对应物相比仍然在很大程度上未被探索。在这里，我们报告了一个高品质的单层NbSe 2薄膜的三角棱镜结构的分子束外延的制造，并通过扫描隧道显微镜，角分辨光电子能谱，和电输运测量，以及第一性原理能带结构计算的电子性质的研究。除了具有3 × 3周期性和低于1.5 K的超导性的电荷密度波（CDW）之外，由于单层晶体中的反转对称性破缺，我们在布里渊区中沿着Γ-K切割观察到相当大的（~0.1 eV）带分裂。这种分裂是高度各向异性的墨水空间，导致带结构中的自旋分裂范霍夫奇点。这些结果表明自旋-轨道耦合和对称性破缺对单层TMD的非常规超导电性和CDW性质的重要性。
Realization of unconventional physical properties in two-dimensional (2D) transition-metal dichalcogenides (TMDs) is currently one of the key challenges in condensed-matter systems. However, the electronic properties of 2D TMDs remain largely unexplored compared to those of their bulk counterparts. Here, we report the fabrication of a high-quality monolayer NbSe2film with a trigonal prismatic structure by molecular beam epitaxy, and the study of its electronic properties by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and electrical transport measurements, together with first-principles band-structure calculations. In addition to a charge density wave (CDW) with 3 × 3 periodicity and superconductivity below 1.5 K, we observed sizable (~0.1 eV) band splitting along the Γ-K cut in the Brillouin zone due to inversion symmetry breaking in the monolayer crystal. This splitting is highly anisotropic inkspace, leading to a spin-split van-Hove singularity in the band structure. The present results suggest the importance of spin–orbit coupling and symmetry breaking for unconventional superconductivity and CDW properties in monolayer TMDs.