NbSe₂ 中堆叠调控的超导性和竞争电荷密度波态
Stacking-tuned superconductivity and competing charge-density-wave states in NbSe$_2$
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中文总结 AI 辅助
研究通过高分辨率扫描隧道显微镜和光谱，发现 NbSe₂ 的堆叠序列可改变电荷密度和超导序。4Ha-NbSe₂ 有两种竞争 CDW 态，引入相分辨分析揭示涡旋及共存机制，还表明堆叠影响超导性，二者均呈现多带配对。
中文摘要 AI 辅助
层堆叠为重塑范德华材料中的集体量子序提供了一条强大但未充分探索的途径。本文利用高分辨率扫描隧道显微镜和光谱表明，仅堆叠序列就能定性地改变 NbSe₂ 中的电荷密度和超导序，同时保持相同的面内原子结构。比较 4Ha 和 2H 多型体，发现 4Ha-NbSe₂ 存在两种与局部应变无明显关联的竞争 CDW 态：单向 commensurate 的 1Qᴾ 相和三角形 incommensurate 的 3Qᴵ 相，且 Qᴵ = Qᴾ + δ。引入相分辨分析直接绘制 CDW 相的梯度并揭示与 1Qᴾ - 3Qᴵ 相界相关的涡旋。这些涡旋通过突然的 2π 相滑移来适应动量失配 δ，为不同电荷序共存提供了一种机制。超导性也受堆叠影响，两种多型体均表现出多带配对。
英文摘要
Layer stacking provides a powerful yet underexplored route for reshaping collective quantum order in van der Waals materials. Here we use high-resolution scanning tunneling microscopy and spectroscopy to show that the stacking sequence alone can qualitatively transform the charge density and superconducting orders in NbSe$_2$, while preserving the same in-plane atomic structure. Comparing the 4Ha and 2H polytypes, we find that, unlike the ubiquitous triangular incommensurate $3Q^\mathrm{I}$ order of 2H-NbSe$_2$, 4Ha-NbSe$_2$ hosts two competing CDW states with no measurable correlation with local strain: a unidirectional commensurate $1Q^\mathrm{C}$ phase and a triangular incommensurate $3Q^\mathrm{I}$ phase, with $Q^\mathrm{I}=Q^\mathrm{C}+δ$. We introduce a phase-resolved analysis that directly maps the gradient of the CDW phases and reveals vortices bound to the $1Q^\mathrm{C}$ - $3Q^\mathrm{I}$ phase boundaries. These vortices accommodate the momentum mismatch $δ$ through abrupt $2π$ phase slips, providing a mechanism by which distinct charge orders coexist. Superconductivity is also reshaped by stacking, while both polytypes exhibit multiband pairing.
