Among Transition Metal Dichalcogenides (TMD), NbS$_2$ is often considered as the archetypal compound that does not have a Charge Density Wave (CDW) in any of its polytypes. By comparison, close iso-electronic compounds such as NbSe$_2$, TaS$_2$ and TaSe$_2$ all have CDW in at least one polytype. Here, we report traces of CDW in the 2H polytype of NbS$_2$, using diffuse x-ray scattering measurements at 77\,K and room temperature. We observe 12 extremely weak satellite peaks located at $\pm$13$^\mathrm{o}$ 54' from $\vec{a}^*$ and $\vec{b}^*$ around each Bragg peaks in the $(h,k,0)$ plane. These satellite peaks are commensurate with the lattice via $3\vec{q}-\vec{q}\,'=\vec{a}^*$, where $\vec{q}\,'$ is the 120$^{\circ}$ rotation of $\vec{q}$, and define two chiral $\sqrt{13}\,a\times\sqrt{13}\,a$ superlattices in real space. These commensurate wavevectors and tilt angle are identical to those of the CDW observed in the 1T polytype of TaS$_2$ and TaSe$_2$. To understand this similarity and the faintness of the peaks, we discuss possible sources of local 1T polytype environment in bulk 2H-NbS$_2$ crystals.
翻译:在过渡金属代谢物(TMD)中,NbS$_2美元通常被视为在任何多型中均无充电密度波(CDW)的顶端化合物。相比之下,近端的超电子化合物,如NbSe$_2美元、TAS$2美元和TaSe$2美元,都至少有一种多型CDW。这里,我们报告在2H2多型NbS$_2美元中CDW的痕迹,使用77美元、K和室温的分散X射线测量值。我们观察到12个极弱的卫星峰值位于2pm$13 $\ mathrm{o}。 近端为$@veSe$2$2$2NbS_2NBS$_2$NbS$2$的顶端。我们报告,这些卫星峰值与3\vec{O}-vexlalalalate $xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx