The nature of superconductivity in ${\mathrm{BiS}}_2$-based superconductors has been controversial while ab initio calculations proposed this system in close proximity to a charge-density-wave (CDW) phase. Using high-energy high-flux x-ray diffraction, we reveal an intrinsic and long-range CDW phase coexisting with superconductivity in ${\mathrm{NdO}}_{1-x}{\mathrm{F}}_x{\mathrm{BiS}}_2$ superconductor $(x=0.37 \mathrm{and} 0.3)$. The CDW wave vector in ${\mathrm{NdO}}_{0.63}{\mathrm{F}}_{0.37}{\mathrm{BiS}}_2$ correspond ${\mathbf{Q}}_{\mathrm{CDW}}=(0.17, 0.17, 0.5)$ and is associated with transverse atomic displacements. Interestingly, this wave vector does not match theoretical expectations based on either phonon softening or Fermi surface nesting. In ${\mathrm{NdO}}_{0.7}{\mathrm{F}}_{0.3}{\mathrm{BiS}}_2$, where the superconducting transition temperature is highest, the CDW satellites are slightly broader and weaker compared to ${\mathrm{NdO}}_{0.63}{\mathrm{F}}_{0.37}{\mathrm{BiS}}_2$, possibly suggesting the competition with the superconductivity. Last, we measure a thermal diffuse scattering across the superconducting transition temperature and find no meaningful changes. Our result suggests the importance of understanding CDW which might hold a key to the superconductivity in the ${\mathrm{BiS}}_2$-based superconductor.

• Received 2 April 2021
• Revised 24 May 2021
• Accepted 25 May 2021

DOI:https://doi.org/10.1103/PhysRevB.103.245120