[论文解读] Modulation of superconducting properties by the charge density wave at the surface of 2H-NbSe2

T. Hanaguri|arXiv (Cornell University)|Jan 22, 2026

Organic and Molecular Conductors Research被引用 0

一句话总结

极低温光谱成像STM显示，2H-NbSe2具有空间均匀的超导能量尺度，但CDW调制的Bogoliubov准粒子权重与表面反演对称性破缺对齐，可能通过Ising型自旋轨道耦合实现。

ABSTRACT

To investigate the interplay between charge density wave (CDW) and superconductivity, we performed ultralow-temperature spectroscopic-imaging scanning tunneling microscopy on the cleaved surface of the layered superconductor 2H-NbSe2. We found that the superconducting-gap spectrum exhibits intricate structures reflecting the anisotropic gaps opening on multiple Fermi surfaces. Notably, none of the characteristic energy scales apparent in the spectral gap show appreciable spatial variations, suggesting that the finite-momentum pairing is negligible. Instead, the spectral weight near the coherence peak is modulated with the same periodicity as the CDW. The maximum position of the coherence-peak-weight modulation coincides with neither the peak nor the bottom of the CDW modulation; rather, it aligns with the center of one of the two inequivalent triangular plaquettes that comprise the CDW unit cell. This distribution pattern of Bogoliubov quasiparticles directly results from the broken in-plane inversion symmetry at the surface of 2H-NbSe2, which may activate Ising spin-orbit coupling.

研究动机与目标

• 研究Charge Density Wave有序性如何影响2H-NbSe2表面的超导性。
• 在存在CDW的情况下，有限动量配对是否显著。
• 在超高能量分辨率下，绘制CDW单胞内的能量尺度与准粒子权重。

提出的方法

• 在剥离的2H-NbSe2表面上执行超低温光谱成像STM。
• 实现约36 μeV的有效能量分辨率，以解析腔隙内结构。
• 在具有高空间细节的CDW领域获取dI/dV和d3I/dV3谱。
• 映射归一化导电性L = dI/dV / (I/V)，以减小设定点效应。
• 通过对d3I/dV3谱进行三次多项式拟合，分析特征谱的能量。

Figure 1: (a) The crystal structure of 2 $H$ -NbSe 2 visualized using VESTA [ 22 ] . A rhomboid prism (thin black lines) indicates the unit cell. (b) Top-down view of a single NbSe 2 layer that breaks in-plane inversion symmetry. A unit cell is shown by a thick black rhombus. (c) and (d) Top views o

实验结果

研究问题

• RQ1 CDW单胞内特征性超导隙能量尺度是否在空间上变化？
• RQ2 与CDW调制相关的超导隙谱权（Bogoliubov准粒子）如何相关？
• RQ3 表面反演对称性破缺与Ising自旋轨道耦合是否会影响2H-NbSe2的表面超导性？
• RQ4 腔隙内细结构与NbSe2的多带、各向异性间隙之间有什么关系？

主要发现

• 超导隙能在CDW域内空间均匀（在数十μeV的尺度内未检测到空间变化）。
• 隙内存在多重细结构，反映多带、各向异性的超导隙。
• 接近相干峰的谱权的振幅随与CDW相同的周期性调制，而非隙的幅值。
• 最大共轭峰权的调制中心在特定的互等CDW plaquettes，而非CDW极大值或最低点。
• 两分量准粒子权重调制模型（分量A与B）能解释能量相关的强度及与CDW的相位关系，符合表面反演对称性破缺及可能的Ising SOC。

Figure 2: (a) A typical STM topograph of the cleaved surface of 2 $H$ -NbSe 2 . The feedback set-point is $I_{\mathrm{s}}=\qty{500}{pA}$ at $V_{\mathrm{s}}=\qty[retain-explicit-plus]{+5}{mV}$ . The areas highlighted in colored boxes represent zoomed-in views in (b) and (c). (b) and (c) Zoomed-in STM