NbS $\boldsymbol{_2}$的2 H和3R多型体的费米学和电子-声子耦合
Fermiology and electron-phonon coupling in the 2H and 3R polytypes of NbS$\boldsymbol{_2}$
摘要：
我们研究了NbS $_2$的2 H和3R多型体的电子结构。角分辨光电子能谱测量的费米表面显示出显着的差异的大小，反映了显着增加的带填充在3R-Nb $_{1+x}$ S $_2$相比，2 H-NbS $_2$，我们归因于存在额外的间隙Nb作为电子供体。因此，我们发现，化学计量比，而不是堆叠的安排，是最重要的因素，在电子和物理性质的差异，这两个阶段。我们的高分辨率数据的2 H相位显示扭结的光谱功能，电子-声子耦合的指纹。然而，耦合的强度被发现是大得多的Nb 4 $d_{x^2-y^2,xy}$特征的带的部分比Nb 4 $d_{3z^2-r^2}$。我们的结果为解释2 H-NbS $_2$的双能隙超导性和“潜伏”电荷密度波提供了一个实验框架。
英文摘要：
We investigate the electronic structure of the 2H and 3R polytypes of NbS$_2$. The Fermi surfaces measured by angle-resolved photoemission spectroscopy show a remarkable difference in size, reflecting a significantly increased band filling in 3R-Nb$_{1+x}$S$_2$ compared to 2H-NbS$_2$, which we attribute to the presence of additional interstitial Nb which act as electron donors. Thus we find that the stoichiometry, rather than the stacking arrangement, is the most important factor in the difference in electronic and physical properties of the two phases. Our high resolution data on the 2H phase shows kinks in the spectral function that are fingerprints of the electron-phonon coupling. However, the strength of the coupling is found to be much larger for the the sections of bands with Nb 4$d_{x^2-y^2,xy}$ character than for the Nb 4$d_{3z^2-r^2}$. Our results provide an experimental framework for interpreting the two-gap superconductivity and "latent" charge density wave in 2H-NbS$_2$.
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