Traces of charge density waves in NbS2

Among transition metal dichalcogenides (TMD), ${\mathrm{NbS}}_{2}$ is often considered as the archetypal compound that does not have a charge density wave (CDW) in any of its polytypes. By comparison, close isoelectronic compounds such as ${\mathrm{NbSe}}_{2}$, ${\mathrm{TaS}}_{2}$, and ${\mathrm{TaSe}}_{2}$ all have CDW in at least one polytype. Here we report traces of CDW in the 2H polytype of ${\mathrm{NbS}}_{2}$, using diffuse x-ray scattering measurements at 77 K and room temperature. We observe 12 extremely weak satellite peaks located at $\ifmmode\pm\else\textpm\fi{}13.{9}^{\ensuremath{\circ}}$ from ${\stackrel{P\vec}{a}}^{*}$ and ${\stackrel{P\vec}{b}}^{*}$ around each Bragg peak in the $(h,k,0)$ plane. These satellite peaks are commensurate with the lattice via $3\stackrel{P\vec}{q}\ensuremath{-}\stackrel{P\vec}{q}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{'}}={\stackrel{P\vec}{a}}^{*}$, where $\stackrel{P\vec}{q}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{'}}$ is the ${120}^{\ensuremath{\circ}}$ rotation of $\stackrel{P\vec}{q}$, and define two $\sqrt{13}\phantom{\rule{0.16em}{0ex}}a\ifmmode\times\else\texttimes\fi{}\sqrt{13}\phantom{\rule{0.16em}{0ex}}a$ superlattices in real space. These commensurate wave vectors and tilt angle are identical to those of the CDW observed in the 1T polytype of ${\mathrm{TaS}}_{2}$ and ${\mathrm{TaSe}}_{2}$. To understand this similarity and the faintness of the peaks, we discuss possible sources of local 1T polytype environment in bulk 2H-${\mathrm{NbS}}_{2}$ crystals.